The Army load was 30 grains blackpowder and I don't know why. It is possible the Army wanted to reduce recoil and have the round go at the same speed as the 45 Schofield. Based on what I have read in Hatcher's Handbook of Revolvers, the Army pistols were made for the 30 grain blackpowder load, because civilian buyers of surplus Army SAA pistols found their pistols would not shoot to aim with commercial 40 grain blackpowder loads. According to Hatcher, the front sights on the Army pistols were the correct height to hit to point of aim with a 30 grain blackpowder load.
But, the standard commercial load was 40 grains of black powder in a balloon head case. I have some balloon head cases and I mean to load them with black powder and test the velocities, I have not gotten around to it. And, I am a bit concerned because I pulled a number of the case heads off sizing the things. Those balloon head cases are weak.
As for blackpowder pressures, if you have the Lyman Blackpowder reloading manual, Lyman had to use lead crushers because copper crushers would not register pressures. Blackpowder weapons had wrought iron barrels and it worked because blackpowder is so low pressure. I have an article somewhere, a look at a Harper Ferry flintlock, and the only steel was the frizzen and spring. The rest was iron and brass.
The early smokeless powders were erratic and blew up the factories they were made in. It took a while for smokeless powder technology to make a stable and consistent product.
For whatever reason, original 40 grain blackpowder loads pushed a 250/255 lead bullet faster (about 1000 fps) than most standard pressure smokeless loads.
