Fouling has been mentioned as if it were a limiting issue with black powder rifles so I thought that I would not just mention that the wax wad was routinely used in all period cartridge military rifles to control it, but also that black powder cartridges were also routinely used in early machine guns.
Of course many mechanical machine guns had multiple barrels to ease the loading stages and raise the rate of fire and they also helped with the cooling but Hiram Maxim's classic recoil operated machine gun began in the era of black powder military rounds and he found that the normal beeswax wad in the cases allowed his gun to function quite adequately. The .45 Gardner-Gatling round he used is not grossly dissimilar to the Martini 577/450 drawn case. It is an illusion that the wad keeps the barrel clean. What the beeswax wad does is to soften the fouling and lay down a film of wax allowing the fouling of each shot to be swept out by the succeeding round and maintain a constant state of fouling which is less than that which will impede or vary the weapon's performance.
Or in the context here. The beeswax wad, contained between two card disks and immediately behind the bullet, will allow a constant performance without variations due to fouling as the fouling is maintained at a constant low level. Fouling is certainly present otherwise I and my forebears would not need to clean the barrel after sessions/actions but it does not impede the continuing performance of the rifle. In my case even when using somewhat dirty firing Vectan powder when not treating myself to Swiss 1.5F (Swiss No4) clean and moist burning powder which is a good match for the fabled Curtis & Harvey No6 and RFG2.
When I was using copy 0.550" Pritchett paper cartridges in my muzzle loading Pattern 1853 rifle the beeswax on the bullet wrapper allowed me to fire repeatedly with no fouling issues to impede muzzle loading. The last would slip down the barrel as easily as the first so the effectiveness was well known long before Martinis were designed.