Handloader Calculations

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.

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

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!

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

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

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

Ballistic Simulator Gun Camera

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.