.41 long colt
I shoot a lot of .41 Colt.....I'd take on more if I could find them/afford them.......
but....and it's a big but...you have to want to do it......as Dingus says .450/ .455 is much easier.....carbide dies, common bullets, plentiful brass/ammo
still, Thunderers and the SAA have their appeal....heeled bullets and shortened cases are a drag and for me only work well with black powder and pyrodex etc...hard to crimp....
Starline brass is easy to get and Rapine makes a dandy hollow based bullet mould.....Trail Boss or any quick pistol powder will bump it up to fit the bore and it will shoot reasonably well...sometimes excellently.......recovered bullets are bore size... .403...up from .386.....****no one will publicly recommend a smokeless load for a black powder era revolver...yet smokless factory ammo can still be found..loaded with hollow based bullets...
Mike Venturino and David Chicoine have good info in their books and Dave Scoville wrote a short article in the Dec. '98 issue of Handloader....
Steve