Pentz wrote on Sep 9
th, 2018 at 9:59pm:
My mistake...it is 515-450. My soft lead bullets drop at .516/455 gr. I will need to get a sizer die for this one. FWIW there are no markings on the barrel other than inspector's stamps, the serial no. and year no. (1874). My rifle has a throat of .533, with rifling at the throat of .488. At the muzzle it measures .475 (12.07)/.510 (12.96).
So,,,it woiuld appear my rifle is 12.17. I'm using 50 Alaskan cases.
Well, yes and no and both. 12,17X42R was original military designation for original rimfire verion. 12,7X44R was/is the original and still in use designation for the civilian CF version. So, ya got best of both worlds, but no rimfire block or rimfire cases.
With soft lead bullets, I would not bother with sizing die. 0,516" is likely just right for your rifle. However, IF first cms of rifled bore is eroded, as it is in mine, you may find a bit larger bullet is useful. Mine gave really nice groups with a 0,520" pure lead bullet intended for a rifle used during USA Civil War.