Possum (the),

We should have known, you have Henry rifling which is best measured with a hole guage otherwise you have some math to do. It looks to me like you have a 9.3 and I'm guessing it was proofed for shooting lead bullets. Is there a bullet type stamp anywhere on the rifle barrel (such as Bl. for lead or K.m.G for Kupfer Mantel Geschoss - Copper Jacketed Bullet)?

Regards,

Buchseman