[quote=that much difference should surely show itself in MEASURABLE recoil, should it not?[/quote]

no larry it won't necessarly show itself in measurable recoil for a couple of reasons. first, 3.5 grains out of the total mass of ejecta (say one ounce of shot plus the powder which is miniscule in comparison) would run the calucalable recoil ENERGY up by something less than one foot lb. and that's using a velocity for the powder of 4700 fps which is typical but if anyone referred to the a-squared manual as i suggested about 11 pages back they'd find that value can be anywhere from 2k fps for low velocity/low pressure loads to 7k fps or more for large belted magnum rifles. if you back off that assumed 4700 fps to something more realistic for a shotgun that less than 1ftlb drops to way less than one foot pound.

and second, if the powder has a different and more progressive burn curve and accelerates the shot charge more slowly down the length of the barrel the FORCE generated is much less. that was also pointed out 11 pages back but for some reason third grade math requiring the multiplication of 2 numbers to come up with a third number seems beyond the grasp of many. everyone resorts to comparing recoil by kinetic energy which is no more valid for recoil than it is for killing effectiveness of projectiles. until everyone can get "kinetic energy of recoil" out of their heads, they're never going to get what's going on when a gun recoils.

and if you don't believe acceleration matters, next time you need to stop your car, drive it into a brick wall instead of using your brakes. same amount of energy is expended but one is going to feel a lot worse (and yes i know that's decelleration but the math is the same, just the sign is reversed).

using kinetic energy for comparing recoil is simplistic, rudimentary, and an inaccurate indicator of what's happening but since that's what everybody has read somewhere in a magazine that seems to be all that sticks.