The lyman handloading books show ballistics in the black powder range, however Accurate Arms show loads that are safe in the replica Sharps, yet deliver the potential of the round.
: My shooting friend now has my .50 X 3-1/4" Shilo Sharps, and routinely uses the 450gr. Lyman bullet ahead of 110gr. of AA4350 or AA3100. These loads are listed for the 550gr. RCBS & could be used with the lighter 520gr. Lyman bullets and so are quite low pressure with the lighter 450gr. bullet, even with the large BP-type firing pin of his Sharps. It is a tremendous load for large North American game, and only gives pressures in the 35,000CUP range. He had an identical gun, but with no freebore, light-stock and hooked butt plate. It was rather murderous with the smokeless loads he'd developed. He's sold that one, and kept my Shot-gun-butt rifle for his hunting rifle. It routinely shoots into 1.3" at 100yds using the tang sight and post front, or adjustable Sharps barrel sights.
; A lighter, but still effective load is 65gr. 3031 and the 450gr. bullet, case full with Kapok, for 1,760fps. This also is an accurate load.
: For BP loads, a PP 600gr. with 120gr. 2F, and card wads filling the case was also an accurate load. With BP, the charge must fill the case with failry hard compression. A grease wad or 60% Beeswax/40% Vaseline is pressed down on the card wad beneath the bullet to keep the fouling soft. This load is a 1.5" for 5 shot load, even though the 36" twist is a bit slow for it. This may not hold accuracy at over 300yards.
: In a stronger gun yet, I am certain a full 2,200fps could easily be given to the 550gr. within about 43,000CUP. Need more? I don't think so. In actual fact, this cartridge, if chambered in a stout double rifle, should match the .500 3" Nitro easily.