Newton says: "for every action, there is an equal and opposite reaction"

I say: pressure drives the acceleration of the payload. Put that together with father Issac's thoughts above. It (acceleration) is traditionally measured over time, by engineers. If there's some other mysterious driver of the payload, besides pressure in a gun, it escapes me.

The "felt recoil test" by Mr. G.T. had how many samples? That was a statistically significant sample of what population? If you took the same number of people, nah! lets say ...the same subjects, and had them shoot a .22 rifle at a quarter flipped thru the air, how many would hit it on the first shot? How many with a .410? 28g? 20g? 12g? Yet Annie Oakley could do it reliably...and Mr. Furgeson can do it with a bow on occasion. Polls and samples that are not statically significant can and do provide misleading information. Even statically significant polls provide only probabilities of outcomes.