Bore butter works great for me in a CVA .54.
Use as hot a water as you can, that way it'll dry itself off from the heat in a few min.
While it's still hot but, after dried. Swab it good with bore butter again.
Clean it real good again in a day or two if you're not going to shoot it right away.
That BP seems to come back before long with crap again. Never had it come back after a good second
cleaning though. It's a good idea to check it and reclean again every few months.
Something that heavy you'll want to use FFg instead of FFF though. Triple F is finer grained for pistol, or lighter cal's.
What projectil's will you be using?
George