Thank you all again for the help. So now I've slugged the bore, driving a Hornady 50cal muzzleloading conical projectile 3 inches into the right bore, starting at the breech end. After popping it back out, I'm seeing what started as .505-.506 now is .496 where the lands impressed/indented the lead. I think these measurements are accurate. Isn't that too small?

The rifles proofs show a 39 bore.

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Last edited by CJF; 09/01/19 03:16 PM.