Been there, done that; I've used 4F up to 40gr in my ROA. It's real peppy with the conicals, but not real accurate. Best accuracy is with the round balls and 40gr of the 4F, once you learn where it hits, as it hits high and I've got the rear sight pegged at the bottom. The 1st time was because I ran out of 3F and had my flinter, so I borrowed some primer powder, started with 30gr and worked up to 40, which exceeds the capacity of the factory cylinder, but I have a pair of Ballistx after market cylinders, that will hold 45gr. My manual says any B/p or sub with 3F being their recommended can be used. 4F is kind of hard to find around here, so I've gone back to 3F or 777, and save my 4F for the flinter.