I measured the Cerrosafe bore castings from flat to the top of the opposing groove, since the Henry bore has odd-numbered flats and grooves. Does this give an accurate measurement or is there a better method?

Mike - I'm curious to know why you wouldn't use smokeless in such a rifle? I understand a 40% Nitro for Black charge is common practice in these old firearms.

Thanks for any comments or advice.

mbatten