Bullet grain help?

[Bartledan]

Bartledan,

I've often thought of including the bullets rotational energy into this equation, although it would really present no *meaningful* "impact" energy data. But in theory - one could sum both the "actual" KE and the rotational KE and get a true KE, correct? Or am I out to lunch on this?

Hey there.
Yes, it's correct, to get the entire picture of the inetic energy, you do have to include the rotational kinetic energy.

Calculating the polar moment of inertia of a bullet will be fun, mind you!

You'll find that the kinetic energy due to rotation is really, really small compared to the linear kinetic energy. Think about it. twist rates in the 1 in 10 range, for a ~.4 inch body is 1 rotation in every 23 diameters, roughly. Not too much.

I did the calculation a long tiem ago for a guy who claimed that guns twist whenyou shot them. I don't have the results but the value was super tiny, in terms of rotational recoil energy, which, due to conservation of energy must be equal to the rotational kinetic energy posessed by the projectile.