The heavy BP loads kick about the same as a 450gr. doing 1,900fps with smokeless loads. The shear volume of burning BP powder produces this, compared to 1/2 weight of smokeless.
: With BP loads, a 550gr. trudging along at 1,450fps is nothing to sneeze at. We know for a fact, if hard cast, they'll exit from a 30" dia. Spruce tree. My bro anchored a moose with his .45x3-1/4" with a 550gr.PP bullet, within 20feet of impact. It staggered that far and collapsed onto it's back, feet straight up, bent at the knees. The .50 hits harder, of course.
: We then went to the .50 Alaskan on McGowen barrels for our Sharps and Rolling Block for eaaier obtained brass and better loading density with smokeless while not being obnoxious to shoot with BP. These, with smokeless or BP still did the job at hand and were easier for obtaining brass and had much improved loading densities. While slightly less powerful than the 3-1/2" case, we've become very satisfied with them.
: Double, eh - nice- but barels too short to properly handle 140gr. BP. If chambered for the .50 Alaksan, it would be a wonderful gun. Plenty powerful enough for anthing States-side & most in Africa with lots of data available. Barnes, Hodgdon, Big Bore Rifle Ctgs.& the big book on Wildcats. They come out at 2.1" and will drive 500gr. at 1,900fps easily with smokeless loads at less than 40,000PSI with over 100gr. total capacity.
: We thought of it as a modern .50/90. It uses .348 Win Brass, blown out straight, an easy forming job with immensley strong, cheap brass that lasts forever.
: The .50x3-1/4" will beat the Alaskan by about 150 to 200fps, but it takes double the powder charge of smokeless(or BP) to do it. Although the biggest .50 case is an interesting to get to shoot well, it is very difficult to get good accuracy with BP. The shorter cases are much easier. This is due mostly to the very dirty burning characteristics of our black powder and a case that seems to need at least 30" or more of barrel to burn it well.
: So, for me, it would be the 2.5"Sharps or Alaskan 2.1" case. The shorter case will come quite close to the longer one.
: At this stage of the game - more food for thought.