GunSim Ballistics Blog

Handloader Calculations

2011-11-29T03:40:00.001-08:00

I have a new app out on Android App Market, an internal ballistics calculator and a reloading "Money Saved per Hour" calculator for rifle, pistol and shotgun. There is also a Bullet Stability calculator using the Miller equations, and a Standard Deviation Chart plotter.
In theory it is platform independent (it is essentially an iPhone app) so it should work on the Blackberry, Symbian-Nokia, and Windows phones too.
The internal ballistics calculator is just the old Powley slide rule, you can't use it to roll your own super hot wildcat cartridges, but you see what seating a bullet deeper is likely to do, that kind of thing.
The reloading savings part is a "What's your time worth" calculator, if you reload a lot you may find that spending twice as much on equipment will save you money if it makes you 20% more productive.
There is a Miller Stability calculator for rifle twist.
You can type in a list of numbers, and calculate standard deviation, to compare the consistency of things, from muzzle velocities to component variability, to group size.
Generally, the Blackberry and Nokia programs are looking primitive to the Angry Birds generation, so I am doing things the easy way with a simpler app development system.

Cosine rules for uphill and downhill shooting aren't accurate.

2011-11-24T23:38:00.022-08:00

The cosine rule says that at 600 yards at 60° is 300 yards at 0°. Which it is, if you are measuring straight lines. But we aren't.
Type it into a ballistic calculator and see how far off you are. Eyes left, -23" 60° at 600 yards, -16" 0° at 600 yards. Off by 7".
Because:
Gravity is no longer operating at 90° to the bullet, so gravity does less (a fishing rod at 60° sags less than a horizontal one, OK?).
Your sights are higher than the bore, the angle changes the zeroing geometry.
The bullet takes longer to get there, and slows down.

So, you have to use a computer. A protractor won't do.

Dual atmospheric conditions

2011-09-17T20:31:00.001-07:00

The Android app now has 2 Atmospherics screens: one for when you zeroed , and one for when you are shooting. This is easier to understand and use than the old system.

This corrects for air density changes between zeroing and shooting.

Temperature affects powder and therefore muzzle velocity, I could add a guesstimate feature to calculate that, but I'd rather not. The barrel flexes during firing. Velocity affects when the bullet leaves the barrel. So the barrel will have flexed to a slightly different position if velocity changes. And you can't really calculate that. Temperature may flex the scope in its mounts.

So dual atmospheric conditions helps, but there are other things going on.

What a Cant!

2011-08-16T16:23:00.005-07:00

This rifle belonged to David Tubbs. He has to do 2 things:

Make sure his reticle is level with the ground.
If the center of the reticle is now 1" to the right of the bore center, aim 1" to the lefton the target. One inch on the target isn't a big deal. In a competition at a fixed range you get sighters, so the offset is no problem, and you can adjust windage instead.

If your crosshairs are centered above the bore, and your reticle is level with the ground, you don't have anything to worry about.

This post is dedicated to Peter Cooke and Dudley Moore.

Scope shimming calculation

2011-08-10T22:47:00.031-07:00

If you run out of scope adjustment at long range you may end up putting a thin metal shim between one of the lower rings and the scope. How thick a shim?
Moa is about 1" at 95.5 yards, 1" at 3438 inches, so 1 Moa = 1/3438" for rings an inch apart, 2/3438" for 2 inches apart.

So rings 3.438" apart, 10 Moa shim, 10Moa * 3.438"/3438 = 0.01" shim at one end.

The rule of thumb on the Internet is:
"Assuming you have about 3 1/2" between the rings, placing a .001 shim under the rear will raise your impact point by 1 MOA."

Which is pretty close.

Free Android Ballistics App

2011-08-10T13:57:00.005-07:00

Here is the free android app, from Android Market.
Android Ballistics

Ballistic Simulator Gun Camera

2011-06-13T23:26:00.000-07:00

Here is the GunSim Camera Ballistic Simulator on Android. You point it downrange, adjust the Field Of View, and shoot things virtually. It is dark, so I'm just shooting the fridge. Should be ready any day now, but the Gun Camera was worth a couple of days of Feature Creep.

Density Altitude and Ballistics Software

2011-05-13T13:25:00.001-07:00

Ballistics programs use pressure, temperature and humidity to calculate the density of the air, because density obviously affects air resistance. You can enter air density directly into the program, usually we use Density Altitude (DA).

DA is a fake height, based on the air density. So if the air pressure at your house drops, your DA increases, even though your house isn't really moving up. Temperature and humidity affect DA too. So pilots use Density Altitude to say, "The air is behaving as though I am at 500 feet".

So the Nokia App and the BlackBerry app support Density Altitude, you type in one number instead of pressure, temperature and humidity. Many weather meters, such as Kestrel, will tell you the DA.

I don't know what pressure to type into my Ballistics Calculator

2011-05-03T18:55:00.005-07:00

If you don't know the pressure in your location, but you do know the height, enter "29.92 inches of Mercury" (or 1013.25 millibars or 760mm of Mercury) for pressure and enter your altitude. The program will use an estimated value based on your altitude. 29.92 inches of Mercury is standard sea level pressure.

It isn't as good as measuring the pressure but it is better than ignoring it.

Two kinds of pressure

2011-04-17T22:36:00.001-07:00

There is "station" pressure - the actual air pressure in the measurement location, unadjusted for altitude. If you have a Kestrel Pocket Weather Meter, you would leave the altitude at zero.

"Barometric" pressure is air pressure adjusted for altitude by a fairly simple formula. This is what weather reports usually use. With the Kestrel Pocket Weather Meter, you would enter the actual altitude.

So if you have a number for pressure, is it Station, or adjusted to sea level? And what does your ballistics program use? If the program has an "Altitude" box, it is Barometric, adjusted to sea level.

If the program has no altitude box, it is Station pressure.

Convert "weather report" pressure (corrected to sea level) to station pressure.

Squeezing the desktop ballistics program into the Android.

2011-04-03T02:41:00.002-07:00

Long range shooting on the bus.

Nokia Ballistcs App for your Rifle Shooting pleasure - $8.49

2011-02-10T21:06:00.007-08:00

The Nokia Ballistics app is now on sale. It is the same as the BlackBerry program, but I had to fiddle with the screen layout to get it looking good.
I really like the new program on my $65 Nokia C3.
It works on over 98% of the phone models Nokia tested.

The Nokia benefits from feedback from the BlackBerry users, and the phone is cheap enough to use as a dedicated ballistics machine.

If you have a different screen size on your Nokia post a message at http://www.mobileballistics.com/, I'd like to have a ballistics app for everybody's phone, so let me know.

Thanks to all for their support!

Zero in the warm, shoot in the cold

2011-02-09T13:09:00.016-08:00

OK, we zero in warm weather, but now it is cold, how do I adjust for that?
Let's look at the warm weather zero. Drop is 0" at 500 yards.
If we drop 59°F, the impact at 500 yards drops 7" in this case:

	Zero in the Warm Here we zero at 59°F at 500 yards.
	Shoot in the Cold Here we change the temperature to 0°F, but we do not re-zero. At 500 yards we are now 7" low. Note that the "ReCalc Zero" is set to "No". If "ReCalc Zero" was set to "Yes", the drop would be 0", as though we we had re-zeroed in the cold.

So this is a realistic scenario, you zero in one set of conditions, and shoot in another. Your ballistic software must allow you to change conditions without recalculating the zero. Most software would recalculate the zero, and give you 0" drop at the zero distance, even if the temperature had changed.
I didn't lower the velocity in this case, the cold powder would actually give you a lower velocity and more drop (probably, although barrel harmonics can do strange things). You would type in the new velocity if you chronographed again in the cold. Plus, a cold rifle and scope may shift things about too.
So if you are shooting in conditions different from your zero at the range, your mobile software can still be useful.

Nokia Ballistc App

2011-02-01T20:40:00.001-08:00

Nokia looks OK, the screen is a bit smaller so much fiddling about was required. Otherwise fine.
If you want a free version you can be a beta tester, use the GunSim.com contact form.

Nokia - it's alive, and got some cosmetic surgery before I let it vist the village.

2011-01-26T16:26:00.009-08:00

Now On sale! $8.49 well spent if you have a Nokia.

Android - Your plastic pal who's fun to be with!*

2011-01-03T23:38:00.008-08:00

This took me almost a whole day to program. It is an Android ballistics app, and it just about works. There are Android Tablet things for $100 bucks as well as phones, so I could have graphics, a bit like the desktop version. It took me about 5 days to get the BlackBerry to do anything, and it will always be ugly. The Android actually has nice little user interface things that work.
So Android GunSim coming soon, unless someone has to go back in time to kill the creator.

Update: The table is working well now, I have yet to start the database stuff.

*Ironically, the Marketing Division of the Sirius Cybernetics Corporation defines a robot as "Your plastic pal who's fun to be with!" The Hitchhiker's Guide to the Galaxy defines the Marketing Division of the Sirius Cybernetics Corporation as "a bunch of mindless jerks who'll be the first against the wall when the revolution comes", with a footnote stating that the position of Robotics Correspondent is vacant.

Chrono distance

2010-12-30T14:49:00.006-08:00

You are on the range and your measure you bullet velocity to be 3000fps at 9 feet/3 yards, using a chronograph. Your need to know the muzzle velocity, to print a ballistics table.
What is the velocity at the muzzle? Your ballistics software will tell you, 3012.9 in this case:

This is where mobile software is so great. You can measure velocity, type it into your phone and you have all the adjustment information at you fingertips instantly. You don't have to go home to your desktop computer.

But if your software doesn't have that feature, how would you work it out?

Put in 3000fps as your muzzle velocity, you lose 14.9fps (3000 - 2985.1) in the first 3 yards.

So estimate the muzzle velocity to be 3000 + 15 = 3015:

3002 at 3 yards is over by 2, so subtract 2 from the 3015:

So now we are 3000.1fps at 9 yards, which is close enough.

Thank heavens for computers!

2010-12-22T17:18:00.002-08:00

From my mailbox:
For example, my math for 500 yds is: bullet drop (in inches) divided by 1.25 inches (where 1.25 is the click value at 500 yds using a ¼ MOA). So if the drop is 64 inches at 500 yds (according to your ballistics table for the REM Core Lokt 223), then 64/1.25=51 clicks; however, your software says it is 49 clicks.

The math is:

**(((4 * 100) / 500) * 64) / 1.0472 = 48.8922842**

If you put 50 shooters in a room with the above question, you could come back the next day and nobody would agree. And probably nobody would be right. So put the pencil and envelope away and use a ballistics program.
(1 Moa is 1.0472" at 100 yards).

How do I use a ballistic calculator to shoot things?:

2010-12-04T15:56:00.000-08:00

You have to get the Big 6: BC, Muzzle Velocity, Sight Height, Zero, Pressure and Temperature.

BC is probably on the Ammo box, or look it up on the manufacturer's website.

Muzzle velocity you measure with a chronometer. Or look it on the Ammo box, or look it up on the manufacturer's website, that will be for a generic barrel length.

Sight height, distance from muzzle center to front sight tip or Scope front center.

Zero, whatever distance you zeroed at.

Pressure and temperature from a weather website for your area. This will vary.

So type in the above values, type in the range to the target, and you will see the drop in inches and the number of clicks (1/4 Moa) to adjust the vertical elevation turret for the drop. Most people aim off for windage, or you can use the number of clicks on the windage section.

If the drop is 6" and 15 clicks, you aim 6" high, or turn the elevation turret in the direction of the scope's "up" arrow 15 clicks. It is good to mark the elevation and windage turret positions when you zero the rifle. If the calculator says go up 30 clicks for a different range, that is 30 clicks fro your zero setting.

Shotgun Slugs and 22LR Ballistics

2010-11-26T14:58:00.004-08:00

Do ballistics programs work with 22LR and Shotgun slugs at Mach 1 (about 1110fps)?

From 0 - 100 yards you are about Mach 1.2 - 0.9 with a 12ga slug. This is a sensitive region (see graph) and most computer programs have very few data points in that range, so they won't work well.
McCoy's book:

Most programs store this graph as a rough approximation. So the steep wiggly part isn't represented well.
Over Mach 1.4 is pretty much a straight line, so the programs are accurate there.

Here is the "GNU Exterior Ballistics Computer" source for G7:
case G7:
if (vp> 4200 ) { A = 1.29081656775919e-09; M = 3.24121295355962; }
else if (vp> 3000 ) { A = 0.0171422231434847 ; M = 1.27907168025204; }
else if (vp> 1470 ) { A = 2.33355948302505e-03; M = 1.52693913274526; }
else if (vp> 1260 ) { A = 7.97592111627665e-04; M = 1.67688974440324; }
else if (vp> 1110 ) { A = 5.71086414289273e-12; M = 4.3212826264889 ; }
else if (vp> 960 ) { A = 3.02865108244904e-17; M = 5.99074203776707; }
else if (vp> 670 ) { A = 7.52285155782535e-06; M = 2.1738019851075 ; }
else if (vp> 540 ) { A = 1.31766281225189e-05; M = 2.08774690257991; }
else if (vp> 0 ) { A = 1.34504843776525e-05; M = 2.08702306738884; }
break;

You have 3 points in the jiggly range around 1110fps, which isn't what you would like. 3 points between 1260 and 4200 is OKish with the straight line.

22LR has the same problem, not enough data for the curve at those velocities.

Why ballistics is important

2010-11-10T23:46:00.003-08:00

From the Internets:
"It still mystifies me that Jack O'Connor and Elmer Keith killed anything. ...(blah blah)...
Sighting your 30-06, 270, 7 Remington or 300 Winchester 2.5" high at 100 yards will let you hold on hair way out to 400 yards which, frankly, if further than most shooters have any business shooting at game."

Here we have some actual data. You are off by 20 or 30 inches at 400 yards, depending on the load of course. Unless you are being attacked by a herd of dinosaurs, this is nowhere good enough way out to 400 yards.
If you spend $500 on your rifle, spend 5 minutes finding out what the drop is at the ranges you will be shooting at, and stick the numbers on your rifle sling.

GunSim price reduced fron $44 to $39.97.

2010-10-19T19:19:00.001-07:00

The BlackBerry Ballistics program uses some of the GunSim code, so this allows a price reduction in the GunSim Desktop Ballistics Program.
The BlackBerry program is about 60k plus about 100k of data, the desktop program is about 1,200k. The mobile program concentrates on practical field use, the desktop program is more about playing around on the virtual firing range.
The Java BlackBerry program should work on other mobile devices, so I'll look into other machines to run it on.
For me it is tremendously interesting and satisfying to make the software, it is great to know that other people enjoy it too.
Thanks for your support!

GunSim Desktop has custom Moa And Mils now

2010-10-19T19:06:00.002-07:00

The desktop program can have mildot reticles with 1/4 Moa clicks. So now you can duplicate your 1/4 Moa clicks not really being 1/4 Moa, and your MilDots not really being 1 Mil.
Too Much Information perhaps, but there it is.

Custom scope click size

2010-10-11T18:32:00.002-07:00

The new BlackBerry Ballistics app has custom scope click size. Why?
"The truth is many scopes can have up to +/- 10% or more error when you actually adjust the scopes. In other words, when you move your scope 60 clicks, it may actually be moving the crosshairs 54 or 66 clicks. You can set up a 'tall target' at 100 yards. Shoot a group at your 100 yard zero then move the scope up 60 clicks and see if it moves the POI precisely 20 MOA or if it's more or less than that." -Bryan Litz.
You can put the rifle in a vice and do it visually, without shooting too. 10" target at 95.5 yards is 40 clicks.
Most scopes are supposed to be 1/4 MOA, 1/4" clicks at 95.5 yards. So your scope clicks are .25 MOA.
But some are 1/4" at 100 yards, which is easier to work with. So your scope clicks are 0.238777 MOA per click.

2010-09-10T17:03:00.004-07:00

The free Blackberry app is being improved, the main screen has been cut down to just what you would want in the field.
I will do a writeup on how to install the app using a USB cable and the BlackBerry Desktop Software.
There is no "Calculate" button, the table gets calculated as you type in the numbers.
It also does Coriolis effect, which is kinda fancy.
So coming in a couple of days.

JBM numbers at the bottom, 0.2" of disagreement at 1000 yards. (BC= 0.3 G1, 2500fps, 100 yard zero, 10mph wind).

Palm Pilot Ballistic Programs

2010-08-29T22:06:00.008-07:00

I spent $30 on a Palm Pilot on eBay, delivered. I'm not worried about bringing a $30 thing into the field, so it will be a dedicated Gun Computer, going beside the laser rangefinder. You can take notes with a stylus pen apparently, so I've decided a Palm Pilot Ballistic computer is A Good Thing.
Programming the thing (on a simulator) was a shock, no floating point math (this is a big deal), and 64kb of heap memory. GunSim was using over 4000kb of heap memory, but I was able to work around it.
I'll see how fast it is when it arrives.
I'll do a free basic version and a fancy version, maybe $30.
So $60 for a fancy hand held ballistics machine, cool. You can play games on it too. It gives exactly the same numbers as the online and Destop GunSim programs.
Exebal has a range estimation screen, that could be useful. Exebal has too may screens for my liking, I don't want to calculate point blank range much, certainly not in the field. Other than that, it looks good.
I assume a handheld is for field use, you just want the adjustments for whatever the range, wind and weather is. Comparing muzzle energies I can do at home. Or 2 programs, one for using with one hand on the rifle, and another for comparing muzzle energies at the bus stop.

Free Blackberry App Improved!

2010-08-13T22:37:00.005-07:00

The free Blackberry Ballistics App now does Mils as well as Moa, and allows you to have more rows of results.
Which is totally awesome!
You type in www.gunsim.com/gunsim.cod into your Blackberry machine, say yes/ok/super/yup to the prompts. Then you click on the icon in the Downloads folder
The app gives you exactly the same results as the GunSim simulator. So you can practice on the simulator online, and have the same information in the field.

Moving targets and lead

2010-08-02T22:00:00.009-07:00

It is much harder to hit a moving target than you think.

So let's insult your intelligence:

If the target is moving at 10fps, and it takes a second to get there, the target will have moved a 10 feet.
If the target is moving at 10fps, and it takes 2 seconds to get there, the target will have moved 20 feet.

If the target is moving at 20fps, and it takes a second to get there, the target will have moved 20 feet.
If the target is moving at 20fps, and it takes 2 seconds to get there, the target will have moved 40 feet.

So, for a given target speed and bullet speed, you lead by the same angle at all ranges.

Assuming the bullet doesn't slow down. At short ranges it doesn't slow down much, and at long range you will be hard pressed to hit a moving target with one shot. Shotgun people often swing to get the speed and aim off at an angle related to the speed. That works.

With a 2680fps bullet, the lead is 1 inch per mph at 50 yards.
So a 4mph target is 4" at 50 yards, 8" at 100 yards.

There is so much nonsense talked about this. People will say "I always lead a deer by 3 feet" without understanding that it depends on how far away the deer is. And what your muzzle velocity is. And what speed the deer is traveling at.

"Zombie at 5 yards, 10mph at 45°, quick, what is the lead?"
No lead at 5 yards at firearms velocities. So pistoleros just need to keep the sights on the target.

2010-07-20T20:37:00.001-07:00

Wind from different directions:

Wind head on, or at your back doesn't count.
Wind from left or right is full strength.

Wind at 45° isn't 50%, it is 75%. So smaller angles have more effect than you might think.

Lee Enfield, smaller groups at longer ranges.

2010-07-15T17:06:00.004-07:00

Some Lee Enfield target shooting is/was done with free floated barrels. As the bullet leaves the barrel, the barrel is on the upswing of its vibration. If some of the bullets are at a lower velocity, the leave the barrel later, and at a steeper angle. At 600 yards, the lower velocity would cause the bullet to strike lower. But the higher angle on the twanging barrel raises the bullet strike to compensate exactly. So stringing due to velocity variation is gone.
In effect, the rifle varies its zero according to the velocity:

The problem is that at the halfway point the variable zero is exaggerating the velocity difference. "There is no such reality as something for nothing".
So the low velocity barrel twang raises the trajectory just right at 600 yards, but way too much at 300 yards.
Windage is not affected, although bad bedding can cause the effects below:

Bullet Drop Video

2010-07-14T22:28:00.003-07:00

I used Google Presentations for this, it isn't bad.

Coriolis Effect on Long Range Rifle Shooting Ballistics

2010-07-07T19:50:00.001-07:00

GunSim Ballistics Key Facts Mailing list

2010-07-07T11:49:00.004-07:00

And now for something completely different. Almost. The GunSim Ballistics Key Facts Mailing list. This means you get a short email with key facts about ballistics each week for a few weeks.
It adds up to a little mini-book on with a condensed overview of ballistics as applied to shooting.

I don't give your email address to anyone else. Some free email addresses don't work with this.

Ballistics for Linux

2010-07-04T15:17:00.003-07:00

Here are some screenshots of the Linux Ballistics Program. I like the Open Source movement, the tools needed for the program's development were free.

Ballistic Randomness

2010-06-25T15:38:00.005-07:00

Where is the center of the group on the right? Somewhere between target center and about and inch high and right I suppose. The rifle is actually perfectly sighted on the center, but you would have to fire more shots to be sure.

When you zero your rifle you shoot a group and guess where the center of the group is. If you are off by an inch at 100 yards, you are off by more than 3" at 300 yards. So if you want to hit with your first shot at 300 yards, you are going to have to fire 7 or 8 cold shots for your zero. So bring a good book :).

Simple Windage

2010-06-23T23:00:00.013-07:00

Earlier we added nail polish marks for scope elevation, is there is simple way to deal with wind?. Yes.
Paint the wind deflection for a 10mph wind at 200 yards on your windage turret cover. As the distance doubles wind deflection quadruples. Let's say you paint "6" on your wind turret as your 200 yard windage. At 400 yards the windage is 4 times that, 24" (Multiply by 4 at 400). At 100 yards the windage is a quarter of that, 1.5".

100 yards	200 Yards	400 Yards
X/4	X	X*4
1.5"	6"	24"

It works in meters too. If you check out a ballistics table, you will see that it is very close.

Cat Box O'Truth

2010-06-20T19:27:00.001-07:00

Ballistics for Hunting

2010-06-15T11:29:00.004-07:00

Hunting with a rife has quietly changed in the past couple of years. You can get a laser rangefinder for a hundred dollars, and a smartphone for "free".
There was a time when, out of ignorance, people would come up with rules of thumb for zeroing. Wind was ignored.
Nowadays you can measure range exactly, look up the ballistics table on a smartphone or luggage tag, and make the correct adjustment to your elevation turret.
If you are still guesstimating, why?

BlackBerry Ballistics calculator software

2010-05-20T22:19:00.004-07:00

Here is the BlackBerry program. This is the standard GunSim calculator engine in pocket-sized style. It has 2 screens, and remembers what you typed in last time. That would be good enough for me. Having 10 saved items would be good, as would a GPS atmospherics lookup. But for a free program it is pretty durn good. Here is a link at the BlackBerry Ballistics calculator software at GunSim. It is at the bottom of the page.

Ballistics for Blackberries.

2010-05-17T21:10:00.002-07:00

This took all day. Blackberries are odd. I suppose I'll do a simple version to give away free with the desktop program. I don't think you need a lot of features in the field, am I missing something?
I could GPS the atmospheric conditions I suppose.

Ballistics for Smart People

2010-05-13T15:17:00.002-07:00

You can put your ballistics chart on a luggage tag, and color code your scope turrets.
There really is no excuse for Point Blank Range, and being too lazy to adjust your scope.

Ballistics Charts and Nail Polish

2010-05-06T20:24:00.017-07:00

If you zero your rifle at 100 yards and the adjustment for 200 yards is 7 clicks, you can use the nail polish you have left over from Halloween to make life easy. One dot for 100 yards, 2 dots for 200 yards, 3 dots for 300. You can see the dots without moving your head by closing your scope eye.

Just in case it wasn't obvious to you.

Acetone removes the nail polish when it is dry. You could color code it. You may as well do your door keys and trigger lock keys while you are in a colorful frame of mind.

(Electric Yellow from the dollar store, with highlighter pens to change the color).

L115A3, 338 Lapua and Craig Harrison

2010-05-06T12:53:00.007-07:00

Here we have Craig Harrison's 8,120ft shot in Afghanistan. I don't know what the temperature was. With no wind, spin drift is over 12 feet, I expect they have ballistic computers to account for that. 1 MPH wind is 70". You would need a quick-adjust canted base or canted rings, 299 clicks is a lot (221 0.1 Mil clicks). The speed of sound is about 1100fps, so we have the dropping below the sound barrier problem too.
Danger Space for a 20" target is only 9 yards at 2700 yards, rangefinding would have to be within 0.25%. You might be able to get 27" groups at 2700 yards, the sound barrier effects would need to be small.

Ranging on non-Ranging Scopes

2010-05-05T10:39:00.019-07:00

Let's say the thick part of your crosshair covers just over an inch at 100 yards at 8x magnification.
See the picture to the left. The black and white squares are 1" across. The crosshair doesn't cover exactly 1" though, so it isn't much use.

Turn the Zoom down to 5 and the thick crosshair now covers 2" at 100 yards. So you can set zoom to 5 and now you have a 2" ruler. At 200 yards your crosshairs will be 4", at 300 yards your crosshairs will be 6" and so on. Simple stuff. If your crosshair covers a 4" thing, the range is 200 yards.
You can use any part of the crosshairs, any measurement units (inch, cm, gopher), and whatever zoom you have on your scope.
If you scope is adjustable, you will be able to find some easy unit to work with.
Laser rangefinders are better, but you might not have it with you.

I used the desktop GunSim ballistics program for the illustration, you can adjust the reticle size on that one.

If you have a Mildot reticle on a 15x scope, and you turn the magnification down to just over 5x, one "mil" becomes 1" at 100 yards. That is kind of math I can do in my head. Assuming a second focal plane scope where the reticle doesn't zoom.

The Answer to Online Ballistics Questions

2010-04-29T15:58:00.013-07:00

People like to ask "What is the drop for 6.5x55 at 300 yards?" and that kind of thing. They get six conflicting replies, partly because they neglect to give all the details you need. Someone posts a badly formatted drop table nobody can read, and it isn't great.

But no more! Just go to the GunSim Save page, enter in the data, click "refresh link", and copy and paste the link into you post. Anyone clicking on the link can print a nice table, everybody goes home happy.

The gobbledygook below is the link, Click here:
http://www.gunsim.com/save.html?name=Winchester%20Super-X%206.5x55%20Swedish%20Soft%20Point&rang=140.0&bc=0.45&velo=2550.0&grou=2.0&zero=300.0&wind=10.0&tars=0.0&temp=59.0&pres=29.92&drag=2&bulw=140.0&alti=0.0&humi=0.0&sigh=1.5&uphi=0.0&tarw=9.0&tarh=9.0&yard=true&tab=2
You can see things like "temp=59.0" in there, that's how it works.

You can bookmark the link too, and can save all your favorite loads as bookmarks. Or email the link to yourself for reference.

High Sights are good

2010-04-22T17:43:00.035-07:00

On a traditional rifle with a curved stock, a 3" high scope makes you lift your cheek off the stock and the scope recoils into your eyeball. So high sights are evil, OK?

No! High sights are good! Mostly!

The dotted line (1" high sights) is further from the gray target area than the solid (3" high sights) line. So the low sights move the trajectory more off target. Same ammo, same zero. At 10 yards 3" sights are worse, but maybe you don't have to aim too carefully at 10 yards anyway. The high sight is better from 50-300 yards. Just what you want for shooting at things that roam about the place.

But the AR-15 has a straight stock, it is designed to have the bore 3" below eye level.
There is no advantage in mounting the sights lower with the straight-stocked M16 family.
You see people with low sights on flattop AR-15s with the butt half off their shoulder to raise the sights to eye level. This is awkward, and places the bullet further off target at the high point of the trajectory.

When the SA80 rifle was introduced with higher sights than its predecessor, British armouries were soon sporting a poster with a soldier looking over a wall through the optical sight with the muzzle touching the wall. The caption read something like "don't do this". So don't do that. Walls are expensive. But otherwise high sights help you hit the target, as long as you have a comfortable cheek weld on the stock.

Extended Maximum Point Blank Range

2010-04-21T15:42:00.005-07:00

Say your Maximum Point Blank Range for your 30-30 is 200 yards. But sometimes you want to shoot at something 230 yards away, without computers and ballistic tables. If you move your scope up a certain number of clicks, you will be on target from 201 yards to some other range. I call this Extended Point Blank Range. The "Extended" range is 10 clicks up, 244 yards in green.

Let's say you don't want to adjust your sights. Aim 5" high between 200-236 yards (shown in dark red) instead.

So if you don't have ballistic tables or software in the field, or you don't have time to access them, it is good to know this kind of thing.

Mildot Rangefinding, Laser Rangefinders and The Danger Zone

2010-04-09T18:41:00.000-07:00

At longer ranges, a small rangefinding error can make you miss the target. For a given target size you will have a stretch of ground called the Danger Zone.
Inside the Danger Zone most of your shots hit the target.
Outside the Danger Zone most of your shots miss the target.
Mil dot rangefinding may not be accurate enough.

Wind

2010-04-09T17:02:00.000-07:00

Wind is something you can neither predict nor control, and it is difficult to estimate. Wind can be swirling in different directions around your bullet's path.
How to reduce wind effects.
You can reduce wind effects by using high BC bullets, at a high velocity.
The more the air slows down the bullet, the more wind deflection you get. So a flat shooting round is a wind avoiding round too. Higher BC bullets are usually larger caliber, and therefore heavier and slower. But BC is more significant here, so the larger calibers tend to be less affected by wind.
Near wind and Far wind.
Is wind at the muzzle more important than wind at the target? Obviously, the sooner the bullet starts to turn off course, the bigger the drift. But, as the bullet slows down wind affects it more. So wind at the muzzle is more important sometimes, wind at the target is more important sometimes.
What does wind do?
Drop a bullet a couple of feet on a windy day. Does the wind blow it sideways much? Of course not. Wind makes the bullet turn in flight (it has to do with spin stabilization). It does not push it sideways much.
How to adjust for wind.

Learn how to estimate wind.
Learn how to adjust for wind angle.
Work out wind deflection in inches for a 10 mph wind, and aim off.

Gravity

2010-04-08T11:43:00.000-07:00

All bullets will drop 4' in half a second of flight. Regardless of velocity.
All bullets will drop 14' in one second of flight. Regardless of velocity.

The difference is that a faster bullet will travel further in half a second. So it will have 4' of drop further away, and will therefore be "flatter shooting".
The forward velocity of the bullet has nothing to do with the downward velocity, because the directions are at 90°.
Perpendicular components of motion are independent of each other.

Like all laws of physics, it doesn't matter what you believe, all bullets drop the same distance in half a second.

What about air resistance? Shouldn't streamlined bullets fall faster? The force of air resistance depends on velocity squared. A bullet traveling 4' in half a second doesn't experience noticeable drag. So , yes, streamlined bullets fall faster, but the effect is very small.

(It is really 44" in .5 seconds, and 162" in 1 second)

The "Rifleman's Method" (for adjusting for uphill/downhill shooting angles) changes your zero.

2010-03-24T17:01:00.001-07:00

In an earlier post I showed the "Rifleman's Method" for adjusting for uphill/downhill shooting angles. It is better than nothing but has 3 problems.

Gravity is no longer operating at 90° to the bullet, so gravity does less (a fishing rod at 45° sags less than a horizontal one, OK?).
Your sights are higher than the bore, which changes the zeroing geometry.
The bullet takes longer to get there, and slows down.

Using a typical 30-30 deer rifle with a scope 1.5" above bore, and using the diagram to the left, at 100 yards uphill distance on 45° you will be 0.5" high (mostly due to sight height), but at 300 yards 4" low (due to reduced velocity). So at large angles, when the bullet is starting to slow down (like a 30-30 at 300 yards) this method isn't enough, you would need to look at a ballistic table. 25° uphill with a 30-30 at 220 yards, this method gets you 0.4" low. (220 uphill is about 200 horizontal at 25°).

The new deskop version

2010-03-22T19:50:00.000-07:00

Hello folks, The new Ballistic Simulator program is ready.

Use your own target, background and sight graphics to simulate how you shoot in the field
Infinite random Scenarios - wind, range, zero, uphill angle, target speed
Zeroing Wizard
Chart different properties of different loads
Save your custom loads
Run offline on a thumb drive on any computer
Export to Spreadsheet
Mil or MOA scope adjustment
6 reticle types, custom crosshair thickness, plus iron sights
Moving targets, changeable wind
Mildot rangefinding practice

It allows you to simulate your shooting environment exactly. Same load, same sights, same target, scaled to the real world. I really think this program will pay for itself pretty quickly, especially if you have more than one rifle. You can set up a simulation of your own riflescope and pet load, then practice adjusting the scope at known and unknown ranges, under varying conditions.

Pesja's 2-number drop table

2009-12-08T22:40:00.000-08:00

Here is a memory trick for memorizing a drop table out to 600 yards (From "New Exact Small Arms Ballistics" by Arthur J Pejsa). Arthur Pejsa suggests a simple way of remembering a drop table. Let's try it out. Perhaps it is more trouble than it is worth.

Zero for 200 yards
Write down the number of clicks to adjust for 300 yards, call it "X", say 10 clicks
Write down the number of clicks to adjust for 400 yards, call it "Y", say 22 clicks
You remember 2 numbers, "X" and "Y"-("X"*2). Or "10" and 22-(10*2).
You remember 10 and 2.

So, 200 yards is 0.....................0
300 yards is 10.......................10
400 yards is 300 yards + 10+10+2......22
500 yards is 400 yards + 22+10+2+2....36
600 yards is 500 yards + 36+10+2+2+2..48

Let's try some examples: Winchester Supreme 223 Rem Ballistic Silvertip BC=0.238

Actual clicks  Estimated clicks, "8" "3"
200 0
300 8..............8
400 19.............8+8+3=19
500 33.............19+8+3+3=33
600 52.............33+8+3+3+3=50

Winchester USA 308 Win Full Metal Jacket BC=0.415

200 0
300 10.........10
400 23.........10+10+3=23
500 37.........23+10+3+3=36
600 53.........36+10+3+3+3=55

Remington Managed-Recoil 7mm Rem Mag Core-Lokt PSP BC=0.388

200 0
300 11...........11
400 25...........11+11+3=25
500 41...........25+11+3+3=42
600 60...........42+11+3+3+3=62

It's a fine line between stupid and clever. - David St. Hubbins So, this almost works, it is clever, but printing a drop table on a luggage tag is probably less trouble. I like the idea of drop as a caliber, the 7mmm Mag above is an 11-25 (like a lever action caliber). So 0-200 is zero (at 100 yards you are 2.1" high), 300 is 11, 400 is 25. That would do for deer hunting purposes, for example. I could probably remember that. Wind would still be a problem.

GunSim.com is looking presentable

2009-10-18T04:09:00.000-07:00

For a simple introduction to ballistics, visit www.GunSim.com. Tons of work, but I'm pleased with it :).

I want something that shoots flat up to 400 yds.

2009-09-23T13:41:00.015-07:00

Nothing shoots flat out to 400 yards.

The simulator now allows the data in the actual link, so let's try it out.

Here we have a link to the ballistic simulator at 140 yards: http://www.gunsim.com/save.html?name=Lapua%20Hunting%20308%20Win%20Mega&rang=140.0&bc=0.319&velo=2510.0&grou=2.0&zero=300.0&wind=10.0&tars=0.0&temp=59.0&pres=29.92&drag=0&bulw=155.0&alti=0.0&humi=0.0&sigh=1.5&uphi=0.0&tarw=10.0&tarh=10.0&yard=true&tab=0

Here we have a link to the ballistic simulator 400 yards: http://www.gunsim.com/save.html?name=Lapua%20Hunting%20308%20Win%20Mega&rang=400.0&bc=0.319&velo=2510.0&grou=2.0&zero=300.0&wind=10.0&tars=0.0&temp=59.0&pres=29.92&drag=0&bulw=155.0&alti=0.0&humi=0.0&sigh=1.5&uphi=0.0&tarw=10.0&tarh=10.0&yard=true&tab=0

In the Picture,
.308 Winchester, zeroed at 300 yards, 2" group at 100 yards.
We are nowhere near close to hitting a 9" target. You have to know what the drop is and adjust. Anyway, now you can save a ballistic scenario as a link, and prove people wrong on the Net! r = range in yards v = muzzle velocity g = group size @100yards in inches th =Target Height tw = Target Width w = Wind speed in mph n = name of load(no spaces) ts= Target Speed z = Zero range in yards

Learn how to estimate wind

2009-09-09T18:39:00.000-07:00

Wind from the right is obviously going to deflect to the left. There isn't an easy way to measure wind in the field. If you have a wind meter, you can play "Guess the Wind Speed" as practice.
Wind speed and direction varies:

With time.
Between you and the target.
With height above the ground, faster as you go higher.

Wind at funny angles, it's more than you think:

If I have a 10 mph wind from the left (3 O'clock), that is a 10 mph wind on the ballistics table.
If I have a 10 mph wind from 2 O'clock, that is a 9 mph wind on the ballistics table.
If I have a 10 mph wind from 1 O'clock, that is a 5 mph wind on the ballistics table.

Wind Direction	Crosswind Factor
From 12 or 6 O'clock	0
From 1,5,7 or 11 O'clock	0.5
From 2,4,8 or 10 O'clock	0.87

Most people use "Kentucky windage", where you aim left or right off the target to compensate for wind. There usually isn't time to adjust the windage knob on the scope. So we need to know 3 things:

Range to target. - Laser, known distance or visual estimation.
Average wind speed between you and the target. - Estimation.
How far to hold your aim of the target for the range and wind speed. - Ballistic table.

Beaufort Wind Estimation Scale

Beaufort #	MPH	Description	Specification
0	<1>	Calm	Smoke rises vertically
1	1-3	Light Air	Direction of wind shown by smoke drift but not by wind vanes
2	4-7	Light Breeze	Wind felt on face; Leaves rustle; Wind vanes moved by wind
3	8-12	Gentle Breeze	Leaves and small twigs in constant motion; Wind extends light flag
4	13-18	Moderate	Raises dust, loose paper; Small branches moved
5	19-24	Fresh	Small trees begin to sway; Crested wavelets form on inland waters
6	25-31	Strong	Large branches in motion; Whistling heard in telephone wires; Umbrellas used with difficulty

Why do snipers have big rifles? - Big Bullets, Big BCs

2009-08-30T23:57:00.000-07:00

Snipers with big bores are compensating for something. Guess what it is? If you double the caliber, and the bullet is the same shape, you roughly double the BC. So larger calibers can have more streamlined bullets. To the left we have a 22 vs a 338 for drop. The 22-250 is closer to line of sight to begin with, because it is faster. The 338 catches up at about 450 yards and has less drop after that. So what? Well let's look at wind. Streamlined bullets (Big BC values) are much less affected by wind. Here we have 3 times the wind drift at 500 yards. About 18 inches of a difference. That's why snipers prefer 338 Lapua to the smaller calibers. They aren't worried about the Lapua going 1 inch higher at 250 yards. They are worried about a sudden 10mph wind blowing them right off target outside 400 yards. They are spot on for elevation with a laser rangefinder and a note of elevation clicks for different ranges. The only way to miss is to misread the wind. And larger calibers have the big BC values. Mind you the increased recoil of the big bullets might require a bigger shooter. So, you guessed right! Technical stuff: D is diameter, M is mass. Doubling diameter cubes the mass if the shape is the same. So if the shape stays the same, BC is roughly a measure of length.

Scope clicks

2009-08-30T14:59:00.000-07:00

You may have been in the position where your shots are going 4" high and left at 200 yards and you want to adjust your scope. You can move the scope a few clicks and see, but ammo is expensive and we don't want the stockpile to get low. Most scopes have 1/4 MOA clicks. One MOA is 1" at 100 yards*. So a click is a quarter inch at 100 yards.

Range/Yards      Click Size, 1/4 MOA
100              1 quarter inch
200              2 quarter inch (half an inch)
300              3 quarter inch
400              4 quarter inch (one inch)
500              5 quarter inch (one and a quarter)
(50              1 eighth inch)

Some scopes have 1/8 MOA per click for finer adjustment:

Range/Yards      Click Size, 1/8 MOA
100              1 eighth inch
200              2 eighth inch (quarter an inch)
300              3 eighth inch
400              4 eighth inch (half inch)
500              5 eighth inch
(50              1 sixteenth inch)

OK, you can remember that. So 4" high and left at 200 yards again. 200 yards, 2/4" per click. Half an inch per click. So 8 clicks=4" on the usual 1/4 MOA scope. Which way to turn the scope knobs? One knob has an "Up" arrow. Turn in that direction to move the bullet impact up. One knob has an "Right" arrow. Turn in that direction to move the bullet impact right. The markings on the scope are talking about bullet impact. So if you are shooting high, move in the opposite direction of the "Up" arrow. Two things to remember:

A .25 MOA click is 1 quarter inch at 100 yards, 2 quarters at 200, and so on.
The markings on the scope are talking about bullet impact.

*Advanced material: One Moa is 1.05" at 100 yards, assume it is 1" at 100 yards. So assuming introduces a 5% error here. If you are adjusting for 4", the error would be 0.2". That may not worry you, but at least you know. If you like, reduce your adjustment by 5%. So 20 clicks would become 19. By the way, you really need to put the rifle in a vise, point it at a 10.5" target 100 yards away (40 clicks) put the crosshairs at the top of the target and go down 40 clicks. Then back up. Then sideways. If the scope is spot on, adjust with confidence. If it underadjusts by 5%, each click is exactly 1/4 at 100 yards, lucky you. If it isn't working, and the vise is solid, then be aware of your inaccurate click adjustments. Check Your Scope’s Click Value–You May Be Surprised

Mildot Windows

2009-07-03T18:24:00.001-07:00

On a mildot reticle there is a square area covered by the thin crosshairs which is 10 mils across. Let's call this the "Big Window". The Big Window is divided into 4 "Small windows". The Big Window is one yard across at 100 yards, Small window 18" at 100 yards. The Big Window is one foot across at 100 feet, Small window 6" at 100 yards. The Big Window is one meter across at 100 meters, Small window 500mm at 100 m. If this is all you can remember, you can do rangefinding if something on the target is a foot across, a yard across, 6" across and so on. Plus on "2nd focal plane" mildot scopes, the area covered by the Big Window is changed by the Zoom knob. So you can turn the Zoom knob down to get a 50" Big window at 100 yards (make a note of this zoom setting), with each mildot covering 5" @ 100 yards. Or a 40" Big window. Or whatever suits you. So you have a rangefinder you can actually remember how to use. Note: First focal plane reticles zoom in sync with the target, so the Big Window always covers the same area at a given range.

Mildot windows for ranging

2009-07-03T17:15:00.000-07:00

OK, let's say the target has a reference of 36" on it somewhere. Height of the target stand, shoulder height of animal or whatever. 36", or one yard is 10 mils at 100 yards, so it covers the "Big Window" exactly. At 200 yards 36" is half the "Big Window", 400 yards a quarter of the Big Window and so on. If you have a known distance of 36" on the target, this is super easy to remember. For an 18" target, use the small window. At 200 yards 18" is half the "Small Window", 400 yards a quarter of the Small Window and so on. So if you have 18" or 36" on the target, you can do rangefinding in a few seconds without computers, paperwork or hard math. If the target is 12" across, it fills the Big window at 100 feet, At 200 feet 12" is half the "Small Window" and so on. A 6" target fills the Small window at 100 feet, you get the idea.

2009-06-29T02:43:00.000-07:00

The new Java program is running as an applet. Very much beta, but it is alive! I'll be fixing it up and doing a screencast to show how you can use it.

Comparing different ballistic programs

2009-06-16T13:35:00.002-07:00

Lets compare the output of different ballistics programs. Test case: BC: 0.3, Muzzle velocity: 2800, Zero range: 300 yards, Pressure: 29.92 in Hg, Wind: 10 mph, Humidity and altitude 0, 59.0 Fahrenheit. We will compare drop and windage at 1000 yards.


Program               Drop"       Windage" @ 1000 yards
Exebal 9.0            -520.6      179.4
eskimo.com/~jbm/      -521.6      179.8
GunSim*               -521.6      179.6
MCTRAJ4**             -521.7      179.9
BallisticSimulator    -520.8      179.8
Sierra Infinity V6    -523.9      179.9
Zdziarski.com***      -510.5      176.2
AppliedBallisticsLLC  -521.6      179.9
JBallistics           -519.9      176.7

Not included:
Ballistic Basics - doesn't have Pressure and Temperature so I didn't bother.
Handloads.com      -517.8        172.8 (Doesn't have humidity)
biggameinfo.com    -522.4        180.1 (Doesn't have pressure)
Shoot! free version - Only uses Remington data

Comment: So, 6 votes out of 8 for -521" of drop, 179.5" windage. Give or take half an inch at 1000 yards. JBM has a good reputation among long range shooters, you can see above that there are free desktop versions which give much the same numbers. So all is well. JBallistics is close to the other six. Sierra doesn't agree. Now Sierra actually makes bullets, but their program does spew embarrassing garbage at times. Zdziarski is a programming libary, so you can't use it directly anyway. At 1000 yards, small changes in pressure and altitude make a big difference. Some programs calculate atmospheric things for you without asking, which is easier to use, but I can't trust the output. Good news is that everybody agrees out to 1000 yards, and Sierra disagree by about a quarter moa. *GunSim is my new Java program, . **MCTRAJ4 MAR. 1987. [TANDY 1000 HX] (pictured above). So the numbers haven't changed in 20 years. ***Jonathan Zdziarski has a ballistics library in C++, programmers only. AppliedBallisticsLLC is Bryan Litz.

Kitty Litter - Bullet drop compensation for ANY caliber.

2009-05-21T18:45:00.000-07:00

OK the Kalinka people say, zero for any distance, and read off the range from the chevrons as multiple of the zero range. Makes no sense, let's try anyway. 200 yard zero, the second chevron is supposed to be 680 yards, it is about 450 yards with 7.62x39mm. The third chevron (1440 yards) is about 8 Mil lower than the first, you would need a very unusual round to get from 200 yards to 1440 with just an 8 Mil drop. The target is 36" wide at 100 yards, or 10 mil across. So the reticle is scaled correctly. Anyway, there might be a specific load that this would work for, but the idea that all loads have the same drop after a 200 yard zero is absurd. Perhaps the 100m(33ft) should have clued me in. I'll line the cat basket with this idea :).

Dragunov Reticle

2009-05-21T12:36:00.000-07:00

Can I put the inverted V things on the Dragunov scope to good use? Probably not, they are too far apart for precision shooting. The other features of the scope are fine. I imported the reticle image from the internet, set the scale at 200 yards using a human size target in the "Measure someone standing up" curve in the bottom left, and tried some 308 Winchester in the simulator. The trick is to try different zero values until the chevrons correspond to useful ranges. 322 yard zero, the bottom 3 chevrons are 600, 800 and 1000 yards (click to enlarge). The left and right grids are Mils (I put a piece of card on the screen and switched to a Mil reticle, yup Mils). So those rugged Russian scopes are potentially useful if you fiddle with the zero. Cool! As you can see the chevrons are a couple of mils apart so they aren't precise enough for most people. You can hunt with the scope, you just won't be using the chevrons much.

Why are the chevrons roughly equally spaced when the bullet path is curvy? A 10" drop at 400 yards is the same angle as a 20" drop at 800 yards, right?. So 4 times the drop at twice the range, is twice the angle. Which happens to be about right for part of the curve at longer ranges.

Elevation for Confused Cats

2009-05-20T14:59:00.004-07:00

Or sheep. Shooting uphill or downhill, just work out what the horizontal range is and use that.

Too confusing for your cat: US Army Field Manual FM 3-05.222 "Special Forces Sniper Training and Employment" Table 3-9. "Compensation Factors Used When Firing From a Given Angle" "Percent of Slope Angle Up or Down (Degrees)" = 45 "Multiply Range by" = 0.7 (eyes left for diagram).

For nerd cats: "Multiply Range by" is the Cosine of the Slope Angle. They actually make Cosine spirit levels to stick on you rifle so you can see the "Multiply Range by" automatically.

But, this isn't correct: http://www.gun-blog.com/2011/11/cosine-rules-for-uphill-downhill.html

Mildots for cats

2009-05-15T22:45:00.001-07:00

Using a Mildot scope for ranging is really simple. Look at the target (click to enlarge). We know it is 10" square. So, if that is 10", what distance between mildot centers? About 14"? Look for 14 in the column on the right, and look up the range on the left. OK, 14.4 is 400 yards. The actual range is 390 yards, let's pretend we don't know that. The drop at 400 yards is 1.4 Mils, so you place the crosshairs 1.4 Mildots above the center of the target. You have the adjustment for wind and target movement lead there too, in the highlighted row. To calculate the drop and windage, you don't need to look at the range. 14.4 inches per mil is a drop of 1.4 mil on the table for that ammo. You could write the "inches per mil", "Drop Mil", "Wind Mil" columns on the back of your hand, that would be all you need.

Estimate target size.
Estimate size between mildots from the target size.
Look up the drop and windage from the table.
Adjust your point of aim.

You don't need computers or slide rules, just tape the table to the rifle. That's it, that's all there is to it. So simple, the cat could use it.

Why is sectional density important?

2009-05-14T00:38:00.000-07:00

For a given caliber, sectional density is a measure of the weight of the bullet. Double the weight, double the sectional density in the caliber concerned. That is all there is to it. It is not a measure of power, penetration or "bullet goodness". It is a measure of weight. Why do gun magazines talk about sectional density as if it were magic? Because they assume you are impressed by mumbo jumbo. sectional density = mass / the bullet's caliber squared Sectional density - Wikepedia Now, heavier bullets are great, but why try to bs with a big word for weight?

Want to see the new program?

2009-05-10T03:07:00.000-07:00

Here is a sneak peek preview of the new program (click to enlarge). It has a super-nerdy "Mildot Ranger" slide rule to cut out and keep. You print out a different slide for each load. In the example, the target is 2 mildots on the scope (left scale) 20" high(next door on the middle scale), so the range is 278 yards, you read off the mildot drop where it says "Target Drop / Mils" (on the right scale). If you have the slide rule you don't need to look up a ballistic table, so you keep one hand on the rifle, and one eye on the scope the whole time. Plus, you practice on the simulator, in the comfort of you own home. Or on the bus, when I get around to the mobile version.

Ballistics for Cats - MOA vs Mils

2009-05-08T13:33:00.001-07:00

Scope knobs usually have 1/4 MOA clicks.

1 MOA is about an inch at 100 yards, so each scope click is 1/4" at 100 yards.

Some scopes have little markers on the scope crosshairs (see below, left), 1 MOA apart. So at 100 yards, you can measure inches by the little markers. You have to set the zoom to a certain value for this to be accurate. Cool. You can work backwards and calculate range. If a 4" clay pigeon is 2 MOA on the scope it is 200 yards away. If a 4" clay pigeon is 1 MOA on the scope it is 400 yards away. Plus, if if the bullet drops 20" at 400 yards, you use the "5" (20/4) on the reticle as the aim point. The other system is Mil.

1 Mil is 3.6" at 100 yards.

The scope may have 1/10 Mil clicks, , so each scope click is 0.36" at 100 yards. Obviously the math is harder to do in your head. With a calculator it doesn't matter. If you are a metric guy:

1 Mil is 100mm at 100m.

So it is a no-brainer for Europeans. A scope click is 10mm at 100m. If you have a 10x scope, 10 centimeters at 100m. Some crosshairs have a "Mildot Reticle"(see below, right), this is just a scale in mils for measuring. If a 110mm clay pigeon is 1 mil across, it is 110 meters away. OK, for mental arithmetic: if you are metric go Mil, Imperial, go MOA. Calculators, it doesn't matter. Some scopes have Mildot reticles and MOA knobs. Gosh. I CAN HAZ KALCLATER? (note: an MOA is really 1.05" at 100 yards. A Mil is really 3.6". Mils in the USMC are very slightly larger). This is for cats, OK?

What difference do multiple BC numbers make?

2009-05-06T22:57:00.000-07:00

Too Much Information about Multiple BC Values: Let's look up a BC numbers for bullet on the Sierra website, .308 dia. 200 gr. SBT :

.560 @ 2600 fps and above
.552 between 2600 and 2300 fps
.555 between 2300 and 1900 fps
.560 @ 1900 fps and below

Sierra gives us different BC values for different velocites, which is great. Most manufacturers would give you one "average" number, maybe .558 or so. What difference do multiple BC numbers make? Let's compare multiple BC values, versus one "average" value. 2800 fps at the muzzle, 2037fps at 500 yards. Same bullet load, just different way of calculating: There are 2 lines there, click to enlarge. You can just see the the brown line (Multiple BC values) behind the black(one average BC value). So are you going to loose a lot of sleep over multiple BC values out to 500 yards? I suspect not.

Mildot Ranger slide rules for free.

2009-05-06T22:26:00.001-07:00

Click to enlarge. (I just finished this, I'll make it look nice later on). Print, glue to a cereal box, cut between the vertical lines (leave some cardboard at the top and bottom to make a window.) The left numbers are target size in mils. Middle sliding numbers, known target size in inches. Left number, drop in mils. Read drop off at the mark on the right. So 20" target covers 2 mils, drop is 0.6 mils for this load (actual ballistics table in this post). The range is actually 280 yards, but.... You don't need to know what the range is, just hold crosshairs 0.6 mils high. The cardboard slide rule is all you need for no-math mildot ranging and bullet drop calculation. You have to print a different slide rule for each load, though, the new Java program does this. Ballistics isn't rocket science! p.s. I'll add windage and drop. But I want to know the range! OK, the markers on the left are 25 yards apart. The bottom one is 100 yards.

Ballistics for Cats - Multiple BC values

2009-05-06T02:27:00.000-07:00

I'll do a few oversimplified ballistics guides. We will start with BC.

BC is a number which tells you how streamlined the bullet is. The higher the number, the more streamlined it is.
A high BC number gives you a bullet that gets to the target faster, so it drops less on the way.
You can get the BC of your bullet by Googling "bc bullet Sierra 303", or whatever. Make some bookmarks.
You can enter the BC and the muzzle velocity into a ballistics program to find out how much you bullet will drop at different ranges. Muzzle velocity is on the ammo box :).
There are different BC numbering systems, such a G1, G6, G7, and so on. The manufacturers use G1, so G1 is fine for normal use.
BC numbers change at different velocities. But it doesn't make a big difference.

Multiple BC's

2009-05-01T19:00:00.000-07:00

Manufacturers give you G1 ballistic coefficients which only work for a narrow range of velocities. Sierra and others give you multiple BC values for different velocities, but most ballistic programs don't use them. I tried Zdziarski's programming library, Exebal, and my old free program with an extreme BC change, and they all give pretty much the same numbers at 500 yards. So this is good, my new Java program will use these guys as a reference. Update: The Java is lookin' good! Range: 500.11851783462333 Drop: -48.81384529231122 Vel: 1644.7919867353637

2009-04-29T02:59:00.000-07:00

I'm working on a new Java ballistic simulator to replace the old one. Mission Statement:

It is the best exterior ballistics program in the world. Because...
It does what the $50 programs do.
It is free.
If it is missing a useful feature the other programs have, let me know and I will add it.
It provides a Head Up Display to simulate what you see thru the sights.
It works on Windows, Macintosh, Linux, and mobile devices.
It actually helps you hit the target in real life, not just weird theory.

It will be the best program in the world, and with your help. If another program does something better, leave a message here and I will improve the program. So I look forward to working with you. It will have flashier graphics, maybe allow you to shoot over videos, and freeze the video when the bullet hits.

How to miss the target.

2009-04-25T18:04:00.001-07:00

This British Para has the back sight on his rifle set for 300m battle zero. See it sticking up? Good thing, with all that terrorism going on. Somebody trained him to do that, and he cares enough to check. The Mumbai police have the same rifle, click to enlarge. People are dying, every back sight is folded down for storage. Nobody cared enough to train these people, and they don't even have the smarts to look through their own sights to see something is wrong. The guy above has had all day to work it out, and he's one of the experienced officers, presumably. Can you find a picture from Google search with a Mumbai police officer with an L1A1 rifle with the sight folded up? Good luck. 1: They haven't been issued with ammunition (no spare mags). 2. They don't know enough to fold the sight up for the cameras to pretend they care. You have to know how your sights work.

Visual Resolution

2009-04-05T15:02:00.000-07:00

The best the eyeball can detect is about 1" at 100 yards, or about 1 minute of angle. Which is a 1" black circle on a white background at 100 yards on a good day. That is 4 1/4 moa scope clicks. With no magnification, less than 4 scope clicks from a ballistic table is invisible. For example: 2750 fps, 150 yard zero out to 200 yards, you can barely see the effect of range without a scope.

Gold Medal match - 5.56x45mm NATO
Bullet Weight   : 77 gr        BC               : 0.31
Muzzle Velocity : 2750 fps     Zero Range       : 150 yards

Range   Height  Hclicks
-------  -------  -------
0      -1.00        0
50      0.67        5 <-- You can barely see 5 clicks
100     1.05        4 <-- 4 clicks is the limit of human vision
150     0.00        0
200    -2.66       -5 <-- You can barely see 5 clicks

Head up bullet drop display, you don't need it with a ghost ring sight out to 200m here: Well, that saves you carrying the laptop to your bunny rabbit hunt, doesn't it?

Did Kalashnikov copy the AK from the German StG 44?

2009-03-26T02:50:00.002-07:00

German StG 44, 1944 version (note "Piston" and "Cocking Handle" parts): Mikhail Kalashnikov's AK-47, 1947 prototype: No, Kalashnikov copied it from the other Russian prototypes: AD by Dementiev AB-46 by Bulkin The Kalashnikov AK-46 (1946) had an SKS-style gas system, it failed the audition: Mikhail Kalashnikov was told the AK-46 wasn't as good as the AB-46 or the AD, bring it up to the same spec as the competition. So Kalashnikov changed to the gas system of his Soviet contemporaries (which was similar to the StG 44, yup). Notice that the AK-46 has a hinged (MP-18 style) receiver, like the StG 44.
Mikhail didn't live in Palm Beach, he designed what he was told to design. The customer is always right, especially when his name is Stalin.
So the answer to the question, "Did Kalasnikov copy the AK from the German StG 44", is "No, he designed what he was ordered to design, comrade".

Rangefinding Made Simple

2009-03-20T22:07:00.000-07:00

Mildot Users

What is a mil?
1 mil of angle covers one yard at 1000 yards. 3.6" at 100 yards. Or 1 meter at 1000 meters. Some scopes have a reticle graduated in mils. The number of inches covered by the mildot is a measure of range.
Lucky metric users know that 1 mil of angle covers 1m at 1000m. 10cm at 100m. Or 4" at 100m, 12" at 300m. I learned to shoot in the Army on metric ranges, so I estimate range in meters anyway.
One mil on your reticle covers 5/6 of a 12" target at 8x magnification. What is the range? How many scope clicks?
I made up the "MilRange" system to avoid mental arithmetic. My ballistic simulator program prints out tables for this.

MilRange is the number of inches on the target covered by one Mildot.
Print the MilRange table for the load you are using, tape it to your rifle, that's all you need. No slide rule, calculator or ability to remember anything is needed. The table has sight adjustments depending on how many inches your mildot covers on the target. Simple as that.

You say 'My mildot covers about 10" of that 12" target, MilRange equals 10.

Read off the scope adjustments or MOA holdoff for drop and wind, and you are adjusted. The range is around 350yards at 8x magnification, but you don't need to think about it.

The table gives you drop and windage in both 1/4 MOA scope clicks and inches. You can have Mils instead of scope clicks if you prefer.

Or "My mildot covers that 12" target plus another 6",

MilRange equals 18".

Look up the table for sight adjustment. The range on 16x magnification is 280 yards, but you just look at the sight adjustment.

Here's the table for the second example. See if you can do it by yourself.

The example is .308 Winchester, 175gr, 2740 fps, BC 0.46, 100m zero, 10mph crosswind at 90 degrees. But you can print a table for any load you like.

You can select a table in either 1/4MOA clicks, or mils. So you can either use scope adjustment or hold off x mils.
Don't use a scoped rifle to estimate range on anything you are not prepared to shoot.

MOA
A minute of angle is a one inch at 95.55 yards, or 1.05" at 100 yards (see below for the exact value).
Most people say "one inch at 100 yards" for the sake of simplicity.
Scope sights usually have adjustment in 1/4 MOA clicks, so if your zero is off by 1" at 100 yards, that would be 4 clicks to adjust. Off by 1" at 50 yards, 8 clicks.
If the scope has 1/2 MOA clicks, off by 1" at 100 yards would be 2 clicks to adjust.
That's all there is to it. Some scopes allow you to set your zero, and then adjust the scope knobs for elevation and windage, You get elevation and windage from a ballistics table.
If the drop is 2" at the target's range, you can aim 2" high instead of adjusting the scope. You can memorize the bullet drop at 100, 200, and 300 yards for your rifle and ammuntion, so you can make the necessary adjustment.
It's worth knowing the amount of windage for a 10 mph wind at these ranges too. 10mph means loose papers blowing around and small branches moving. It also means at right angles to the firer. If the wind is at an angle, you guesstimate what proportion of the wind is at right angles to the direction of fire.
The wind accelerates the bullet in the wind direction. So doubling distance more than doubles wind deflection.
This makes is long-range shooting difficult, you may have to get closer to the target if it is windy.
Nerd Alert:
Take a scientific calculator. Type in 1, TAN, multiply, 60, equals. The answer is 1.04730389569305514590773371318367, which is the number of inches covered (or subtended) by a minute of angle (MOA) at 100 yards.

Mil-Ranging on non-Mildot Scopes

You can use a non-Mildot scope to estimate range using this program. Say your fixed 4x scope crosshairs cover 0.4" at 25 yards. Run the program with different scope magnification numbers (5.6x in this case) until the MilRange at 25 yards is 0.4" (or 4" at 250 yards).
So now you print the table, and you can use it to estimate range, pretending the crosshair width is a Mildot.
If your scope is adjustable, you have to use the same magnification for when you estimate what your crosshairs cover, and when you estimate range with your printed table. Otherwise it doesn't work.
Don't use a scoped rifle to estimate range on anything you are not prepared to shoot. You can carry a $25 compact scope in you pocket and use that for ranging in the field.

What distance do you guys sight in your Eotech's? I will be shooting out to about 200-300 yards.

2009-03-14T03:47:00.000-07:00

Well, here is an Eotech reticle, 1 moa dot. Wind 4mph->, stationary target. Sights 2" high. Using the Point Blank Range function, a A 260yrd (same as 35yrd) zero gives you 3" high at 150yrd, 3" low at 300yard, easy to remember. Note: 3" high at 150 is twice the angle of 3" high at 300.

5.56 Radway Green ( RG 97 ) ss109
Altitude        : 0 ft         Temperature      : 59  °F
Bullet Weight   : 62 gr        BC               : 0.304 
Xwind Speed     : 4 mph        Xwind Angle      : 90 °  
Muzzle Velocity : 3122 fps     Zero Range       : 260 yards
Target Speed    : 4 mph  

Range   Height  Hclicks     Wind  Wclicks      Vel   Energy      TOF     Lead  LClicks    
-------  -------  -------  -------  -------  -------  -------  -------  -------  -------    
   0    -2.00        0      0.0        0   3122.0   1341.7    0.000      0.0        0
  50     0.74        6      0.1        1   2960.8   1206.7    0.049      1.6       12
 100     2.49       10      0.4        1   2805.6   1083.5    0.101      3.3       13
 150     3.14        8      0.9        2   2655.6    970.8    0.156      5.1       13
 200     2.55        5      1.6        3   2510.6    867.6    0.214      7.0       13
 250     0.57        1      2.5        4   2370.0    773.2    0.276      9.0       14
 300    -2.95       -4      3.7        5   2233.9    687.0    0.341     11.2       14
 350    -8.22       -9      5.2        6   2102.2    608.4    0.410     13.4       15

What's new!

2009-03-08T03:13:00.000-07:00

After a few years, I have come back to my ballistic simulator program with some upgrades. First thing is a Bullet Drop Compensator. This shows how high or low the bullet will hit relative to the sights. For example, a 9mm Glock : (Click to enlarge picture) The coloured numbers show where you need to aim for 5, 10 and 15 yards. The white circle at the bottom shows a 5 moa group circle where the bullets will actually hit (Sights zeroed for 5 yards, target at 16 yards, so we hit low). I should make the numbers bigger :). So drop isn't a huge deal at normal handgun ranges. I'm open to suggestions for new features. If your suggestion is sensible, I'll try to put it in.

GunSim Ballistics Blog

Handloader Calculations

Cosine rules for uphill and downhill shooting aren't accurate.

Dual atmospheric conditions

What a Cant!

Scope shimming calculation

Free Android Ballistics App

Ballistic Simulator Gun Camera

Density Altitude and Ballistics Software

I don't know what pressure to type into my Ballistics Calculator

Two kinds of pressure

Squeezing the desktop ballistics program into the Android.

Nokia Ballistcs App for your Rifle Shooting pleasure - $8.49

Zero in the warm, shoot in the cold

Zero in the Warm

Shoot in the Cold

Nokia Ballistc App

Nokia - it's alive, and got some cosmetic surgery before I let it vist the village.

Android - Your plastic pal who's fun to be with!*

Chrono distance

Thank heavens for computers!

(((4 * 100) / 500) * 64) / 1.0472 = 48.8922842

How do I use a ballistic calculator to shoot things?:

Shotgun Slugs and 22LR Ballistics

Why ballistics is important

GunSim price reduced fron $44 to $39.97.

GunSim Desktop has custom Moa And Mils now

Custom scope click size

Palm Pilot Ballistic Programs

Free Blackberry App Improved!

Moving targets and lead

Lee Enfield, smaller groups at longer ranges.

Bullet Drop Video

Coriolis Effect on Long Range Rifle Shooting Ballistics

GunSim Ballistics Key Facts Mailing list

Ballistics for Linux

Ballistic Randomness

Simple Windage

Cat Box O'Truth

Ballistics for Hunting

BlackBerry Ballistics calculator software

Ballistics for Blackberries.

Ballistics for Smart People

Ballistics Charts and Nail Polish

L115A3, 338 Lapua and Craig Harrison

Ranging on non-Ranging Scopes

The Answer to Online Ballistics Questions

High Sights are good

Extended Maximum Point Blank Range

Mildot Rangefinding, Laser Rangefinders and The Danger Zone

Wind

Gravity

The "Rifleman's Method" (for adjusting for uphill/downhill shooting angles) changes your zero.

The new deskop version

Pesja's 2-number drop table

GunSim.com is looking presentable

I want something that shoots flat up to 400 yds.

Learn how to estimate wind

Why do snipers have big rifles? - Big Bullets, Big BCs

Scope clicks

Mildot Windows

Mildot windows for ranging

Comparing different ballistic programs

Kitty Litter - Bullet drop compensation for ANY caliber.

Dragunov Reticle

Elevation for Confused Cats

Mildots for cats

Why is sectional density important?

Want to see the new program?

Ballistics for Cats - MOA vs Mils

What difference do multiple BC numbers make?

Mildot Ranger slide rules for free.

Ballistics for Cats - Multiple BC values

Multiple BC's

How to miss the target.

Visual Resolution

Did Kalashnikov copy the AK from the German StG 44?

Rangefinding Made Simple

Rangefinding Made Simple

Mildot Users

**(((4 * 100) / 500) * 64) / 1.0472 = 48.8922842**