Originally Posted By: David Furman
What I want to know is if Mike and Jim's recoil calculators give the same results. If not, then of course I want to see everyone fight--sorry "discuss" which one is correct.


You make a great straightman, McT. wink

Actually, I've already compared them and 1)no, they don't agree because 2)I suspect the one I've used (from 2 sources) is geared to rifles, but don't say so. The one Legg linked to has separate calculators for shotguns and rifles. Those two give different answers for the same values.

I suspect the reason the shotgun calculator gives a smaller answer is that it assumes an escaping gas velocity of ~2,000 fps as opposed to ~4,000 fps for a rifle (4-5x the peak pressure).

But, directionally, they are the same, though the magnitude is different. Whereas the rifle calculators suggest ~14% FRE increase with 10 grains more powder, the shotgun calculator suggests ~9%....still greater than the 4% increase you'd see from 10 grains more lead.