[Unclenick]

I did some experimenting with Hodgdon Clays and VV N310, which are very fast, in the 1911, and found that for a given produced MV, perceived recoil was actually lower. The quick kick of the low weight charges got the slide moving inertially, but because the bullet was out of the muzzle sooner than with Bullseye or Universal Clays, the muzzle exit occurred in an earlier portion of the unlocking cycle. The result was the muzzle didn't climb as much so the recoil was straighter back into the hand where it isn't as noticeable.

A lesser factor (in handguns) is that in a straight wall case about 70% of the powder is pushed forward with the bullet, burning from the bullet base forward, so a larger weight load of slower powder adds to the mass being accelerated. It then keeps the pressure up longer so the muzzle pressure is higher at bullet exit, and rocket effect from the gas accelerating out of the muzzle is thus increased. Both factors add to the total recoil. The effect is much more dramatic in rifles, but makes some contribution even in .45 ACP loads.