Really, it would have been a challenge. The various different mechanisms for automatically unlocking and reloading a firearm could likely work at the lower pressures of black powder, powered by the recoil or residual gas pressure in the barrel. But smokeless or nitrocellulose-based propellants convert mostly to gas, on ignition. Black powder, on the other hand, leaves behind a lot of solids, which are aptly called fouling: because that is what they do. Build-up of fouling obstructs the loading of muzzleloaders and obstructs the chambering and extraction of cartridges in breechloaders. This last is a serious issue: some rifles, like the early Trapdoor Springfield, had pretty brutal cartridge extraction, and some, like the Martini Henry, had weak cartridge cases, so as fouling built up, cases would often tear and jam the gun until they could be pulled out. An auto-loader, processing a lot of ammunition, would have had more difficulties. One that used gas from the barrel to move an operating rod, or piston, to auto-load (like the modern AR-15, M1 Garand) would have had another mechanism to be fouled.

Hand-cranked auto-loaders like the Gatling Gun and and Agar Gun had less trouble with fouling- but they were still susceptible to its problems, the Agar especially.