That looks just like my 1916 Mark 111.
One thing about shooting BP, is that it heats the barrel up faster than smokeless. It also kicks more than an EQUIVALENT load of smokeless. This is VERY "evident" in shotshells with a SxS where holding the tubes is normal.
Shooting jacketed bullets quite cleans the bore each shot. BP and jacketed, shoots usually VERY accurately, even compared to good cast bullet shooting.
The "plug" used in the original load, weighed 70gr. The only way to load that was to use a compressed pellet, put into the case before it was formed. A pellet was put into the straight walled case, then a jute wad was placed on top of that, then the neck was formed then the bullet loaded.