I for one would start out with some B, to get a reference load - after all, that's what the rifle was made for. Next - chamber cast: Most Sniders I know of have a groove dia. of at least .590, so that .582 bullet with 4198 could just be a case of the bullet being too small, and not able to build up enough resistance. Also, 4198 does sound like a bit slow-burning for the round, aggravating the issue...
BP is the propellant of preference IMO, and I'm not talking the fake BP's either. Maybe you should get the storage box and fill out the papers...