Originally Posted by
TurnipEaterDown
Recoil acceleration curve: The rate at which the firearm accelerates in recoil.
The rate of change in acceleration over time is called, in engineering terms, "Jerk" (no lie, though I learned this 35 years ago, so, brain cell half life...)
A comparison of loads from two distinctly different firearms, say a 338 WM with a mid range bullet, and 45-70 w/ heavy bullet, even IF loaded to produce the same momentum or energy, and the in the same weight of gun, will not create the same recoil characteristics as the time-pressure curve under the 338 bullet differs than that of the 45-70 in this example.
The Force applied to the bullet base by the gasses is also applied to the gun, and wants to move the gun in the opposite direction of the bullet (recoil).
So, you get a different "feeling" recoil because the the acceleration of the bullet is different.
It is not a total energy number or a total momentum number of the bullet that tells you much about recoil, it's a combination of things. Nice explanation of this in the A-Square manual "Any Shot You Want".