If your rifle has Ballard rifling (normal rifling) it will handle cast bullets well. If it’s one that has the Micro groove rifling you’ll need to load jacketed bullets. I had one with the Micro groove type and cast bullets both hard to soft wouldn’t shoot very good.
Actually, I had a question about that very issue. I've been looking at the current Marlin SBLs in .45-70.
What rifling do the SBLs use, and will they shoot the hard cast 405gn boolits accurately (specifically the COATED 405gn HCs)? I'll be sticking with that weight of HC slug almost exclusively.