Trailrider - very well written. Some time ago, when I was shooting a .45 3 1/4" Sharps, I perused an Accurate Arms loading manual as they printed data for these guns. Their data then (RED BOOK) started with a factory-type black powder charge. IIRC, the .45/70 was loaded with 70gr. 2F and a 405gr. Lyman bullet, probably #457141 that developed 22,000PSI on their pezio machine. What is really interesting, is that the .45/90, with it's 300gr. and 90gr. of 2F developed 28,000PSI and the .45 3 1/4" with 120gr. and a 500gr. evened out at 30,000PSI. Thus, they held those pressures with their smokeless loads. the .50 3 1/4 also ran 30,000psi. using 140gr. 2F and a 500gr. bullet.
Lyman's book, the #46th manual also lists pressures for the black powder loads in .45 cal. but did not pressure test their .50 cal loads. Their data closely follows that of Accurate Arms in the long .45, but their .45/70 data is lower, however is CUP, not PSI. further note, they list their .45 3 1/4 loads for use in replica Rolling Block and Sharps rifles. At that time, only the Navy Arms RB and the Shiloh and CSharps Arms Sharps were the rifles referred to. Their 300gr. data for the noted .45 3 1/4" was loaded to 35,300CUP uisng IMR3031 not psi but CUP. This pushed a 300gr. Sierra bullet at 2,409fps, yet the next lower pressure using H4895 ran 2,742fps at 34,100CUP.