Back when there was really good ammo being made in CanadaAND sold to he public, C-I-L used to load the .43 Mauser with smokeless as a standard hardware-store item. It sold for $3.65 a box of 20, which was a bit of a shock: I only paid $3 for the Carbine!
I took one apart once, just out of curiosity. The powder was irregular, looked like tiny little balls of cat-food or something: it was PINK. It was VERY fast stuff, too.
A lot of guys use SR-4759 in these rifles. You can use SR-4759 in most black-powder cartridge rifles if you load the SR-4759 at 38 per cent of the black-powder charge. Being that the Mauser round was, in the US system, a .43-77-386, you could load 29 grains of the SR-4759 and you should get original performance at original pressures. The stuff is so very quick that you really shouldn't require a wad, but the rifle is always the boss.
SR-4759 is the very last of the old-time 'Bulk" powders, although it can't actually be loaded bulk-for-bulk. It DOES work very well as a Black substitute at the 38-percent level and it usually doesn't leave unburned powder grains all over the place, as will IMR-4198 a lot of the time.
DO have fun Mousering!