Pudge
Member
Correct and that is why I state that the formulas are estimating an average gas velocity due to the difficulty of actually calculating it (CFD modeling anyone). Most of them estimate the average gas velocity based on some multiple of the muzzle velocity and the only way to get exact measurements is with a ballistic pendulum or a recoil force measure system.
Again the differences are real but relatively low percentage of the total recoil impulse in a pistol cartridges due to the ratio of bullet mass to propellant mass. 20gr of propellant pushing a 125gr bullet even if the average velocity of propellant gas is actually 2x in our short barrel instead of the standard formula estimate of 1.5x still only changes things by about 6%. Again you are correct with a short barrel you expect and we can measure that the propellant play a slightly larger role in the recoil impulse then it does in a longer barrel but it is still relatively small do the fact that the bullet is so much heavier than the propellant. In rifle cartridges this ratio starts to get more meaningful. In shotguns its nearly negligible in many cases.
Where does the energy of the gas velocity go in those 2"?