I hesitated to answer because Boltman seemed to be against the cartridge I would choose if it were my rifle. Since no one spoke up, here is what I think. I would go with the British 375 Flanged 2 1/2 inch. The .375" bullets are available from several sources, and I am prone to shoot cast bullets also. As far as donor cases are concerned, .303 British cases are fairly available. If They shorten too much in fireforming, slightly less available 30-40 Krag cases should work. I often use short cases by loading the bullets "out" anyway.
Mike
Mike - I am more open to the .370/.375 (.375 Flanged 2.5 inch) that you suspect. Certainly of great appeal is that fact that is the original chambering and it would match the information engraved on the floorplate. One trick is to find a barrel maker set up to provide that chambering.
I load for many obsolete calibers, so I'm not afraid of that aspect. I'm confident .375 Flanged 2.5 inch brass is a lot easier to find than brass for .38-45 Bullard (another use for .303 British cases).
I appreciate the responses.
