A person who has "felt" recoil doesn't need to prove it. He already knows what he felt. On the other hand, neither can he predict what others will feel, unless he has run a correlation of "felt" recoil with them.

It seems to me that current measurements and calculations of recoil do not satisfy all perceptions of recoil by all individuals. I think we lack an objective measure that will more accurately predict "felt" recoil. Another research project for retirement.