Originally posted by revdocdrew:
My usual load for that 20 is 3/4 oz at 1200, 1/8 less than the AA but the same fps. I wouldn't presume to attempt to explain the perceived difference (assuming that the thin plastic case entering the forcing cone contributes little to increased pressure) but there is a marked difference.
I wouldn't know what is causing the difference either, but since you do notice such a marked difference then I think you are right to steer clear of those loads. It would be interested to see what happens to your perceived recoil with those same AA cases loaded differently. Or with a close replication of that load in a shorter case.
(I'm wondering if it is something particular to that case in your gun's chamber causing the change. Or if it is attributable to the other differences between loads.)
Certainly understanding perceived recoil is much more complicated than calculating foot pounds. Any number of things come into play from powder burn rates, to gun fit, to barrel harmonics, to sound, etc. etc. to quote Churchill (I think) "It is a riddle wrapped in a mystery inside an enigma."
I also think recoil expressed merely as foot pounds is not adequate to understand recoil-damage to a gun. Two loads generating equal muzzle velocities with equal ejecta (same calculated recoil) may effect the gun itself differently...
