
Need help with ammo math
I've been trying to figure out how to calculate muzzle energy on a particular round.
I would assume when we refer to energy we are referring to momentum (velocity * mass).
So.. that being the case, most bullet weights are measured in grains. From what I gather there is 7,000 grains per pound.
So I would think I could calculate grains to pounds by taking the grain and dividing it by 7000. So a 35 grain bullet would be .05 pounds. Does that sound correct?
So then I should be able to get feetlbs by multiplying .05 by velocity. Unfortunately, this math doesn't work. Every time I try this, I'm way off from the manufacturer's listed energy rating. Not even close.
What am I doing wrong?

You're using the formula for momentum (mv).
You want the formula for kinetic energy (mv^2).
Matt

m x v2 / 452000 = energy [452000]is rounded off]
so 125 gr going 1100 fps is 125 x 1210000 /452000 =334.62 foot pounds of energy
if the mass is already expressed in grains, there is nothing to convert.

Ok.. I think I understand now. What I was trying to figure out was exactly how much difference there is in energy from a pellet gun vs. a real firearm. I'm using a standard velocity .22LR as a comparison. Typical energy is 102 ftlbs.
So, if I have it calculated correctly, a BB pistol using a 7 grain pellet at 450 ftsec, should be about 3.13, meaning a .22LR is about 32.5 times more powerful.
and a BB rifle shooting at around 1,000 ftsec puts the energy around 15.5 ftlbs. So that means a .22LR is still 6.5 times more powerful.
I haven't been able to figure out the grain of an airsoft or paintball gun quite yet.. Those are usually measured in grams. But I just thought it would be interesting to make a chart showing the comparative power between airsoft, paintball, BB, pellet, and .22LR. Then maybe add in some larger calibers of real firearms too.