Algodoo

Awesome! Its very good code and it seems to work very nicely!

The only problem I see is that, as far as im aware, you dont want bullets to over-penetrate. If its not true I'd love to learn how it works

The key to the overpenetration issue is that you can control the stability of the round by a constant:
{ 1 + (vel(0) * vel(1)) ^ (2) * C }
Where C is a stabilization constant. Also, if the bullet already unstable and rotating inside the barrel it would not help because starting angle velocity != 0.
It actually helps with some firearms that have a problem with squib shots or bullets not going straight through the barrel.