I heard that black powder would more easily foul barrels. The maxim was the first 'practical' machine gun, so what measures had to be taken for the faults of black powder?
The most common chamberings for the Maxim Gun were .303 British, 7.92x57mm, and 7.62x54mmR. All are smokeless cartridges, used in both World Wars.
The mid-1880's, when the Maxim Gun was designed, were when smokeless powder became widespread.