Very True. All the guns in game use smokeless powder.
But the courier could make black powder and lead bullets if the game would let him,
given the tech available to him.
Oh yes, and the cowboy guns would easily run black powder and lead bullets no problem.
Any doubts? Then look up cowboy action competition.
Hell, alot of the guns in the game were
designed for black powder. Here's a short list:
.357 magnum revolver (Colt 1873 SAA)
Cowboy Repeater (Winchester 1866)
Trailer Carbine (Winchester 1892)
Brush Gun (Marlin 1895)
Lever-action Shotgun (Winchester 1887)
Pump shottie actions are all essentially the same as the first Winchester 1893
Bolt action hunting rifles are essentially the same as the Mauser rifles from the 1890's
Most all modern revolvers differ very little in their design details from those designs at the end of the 19th century.
Semi-auto shotguns most likely still use the long-recoil action first designed by Browning in the 1890's.
Cartridges you could reasonably make into black powder:
.22LR
.357 Magnum/.38 Special
.44 Magnum and Special
.45-70
All shotgun shells
9mm (a bit of a stretch, but both the pistol and the SMG would probably still work, possibly with stighly weaker springs)
10mm (same as above. SMGs using blowback and pistols using recoil would still work, just might need a little tinkering)
.50MG (hey, it would work. I know: who would want it?)
I've probably missed a few, but basically, not only would some of the weapons easily handle black powder, they were designed for it. You could easily add black powder rounds, as the above poster suggested with a downwards DAM modifier and an upwards CON modifier. It'll be a real [censored] to redo all the firing animations to model in all that smoke on the battlefield though, so for that reason alone, I would not do it. Stick with smokeless.
-Gunny out.