re: #188 jcm

Barrel length affects muzzle velocity, as does powder load, powder burn rate etc…

Basically a too short barrel the gasses don’t have to to accelerate the round to the maximum possible before the muzzle is reached. Too long and the gasses have expanded and the friction in the barrel will slow the round.

The weight, aerodynamics and muzzle velocity all effect how much energy is delivered down range and how much is lost going down range.

in other words it’s not a given the M16 has a higher velocity than the shorter M4 all else being even?