[velocette]

The rifle has .38 CFC stamped on the underside of the barrel just forward of the foregrip.
The rifle would chamber a .38 S&W round. Definitely the early .38 caliber which was .375" not the ..357 of the "real" .38s.
Don't have a clue as to why Whitney used .38 CFC unless it was to avoid using someone elses cartridge name. The rifle works just fine with mild loads of Accurate 1680 propellant and Missouri's 120 gr .314" RNFP bullet.
The rifle did NOT like black powder, shooting patterns no matter what bullet I used. l