Unfortunately, all black powder was not equal--any more than all smokeless is equal. So you go back to the black powder days and you add a bit of mystery to the recoil energy of those guns. That is, unless you know the muzzle velocity in addition to the shot charge.

I'd also note that in 1913, SAAMI did not yet exist. (It dates from the mid-1920's.) And prior to SAAMI, in this country, proof and service pressures were not yet regulated and standardized. Once they were, and once we'd switched to smokeless as a propellant, the hottest load available for the 2 5/8" 12ga was--and I have to make a correction here (print is SMALL in my old Shooter's Bible!)--a 3 1/4 DE, 1 1/8 oz load. 1255 fps, which I find listed at the same recoil energy I quoted before: 22.7 ft/lbs. So you're still jumping the recoil 50% just to get to the then-hottest 2 3/4" 12ga, 3 3/4 DE, 1 1/4 oz (1330 fps) at 33 ft/lbs. Not to mention the current hottest 12ga loads, which deliver over double the recoil of the hottest 2 5/8" smokeless loads.

I don't think anyone is saying recoil is a benign force. Obviously, however, since both SAAMI and CIP set pressure standards (and not recoil standards), neither is pressure. Best for the safety and integrity of our vintage guns to stick to loads for which they were designed--AFTER the establishment of an organization in which arms and ammo makers voluntarily cooperated to set standards. Better than talking about what Davey Crockett shot in Old Betsy.