So I have a Webley. Shaved to .45 acp. Bore slugs a generous .457. Even a fairly heavy .45 bullet has a pretty big jump to get to the rifling.
I also have a 370 gr Lee mold. Just loaded a dummy. Reaches the end of the cylinder with about 1/4 of it into the case.
This has possibilities, but load data is going to be entirely up to me, I would think.
I'm thinking of perhaps using 2400, and going from there... assuming no one has data on this combo (doubtful!) what powder would you use to start light and work up?