I've got a trivia question for our experts out there.

I'd always wondered why bore rifles seem to be marked "off" by one gauge. Not withstanding the poetic license involved in large bore rifles (most nominal 4s really being 5-6 bore, etc), I've seen bunches of 12-bores('proper' .729"-.745" size) proofed at 13, my own .778" 10-bore is marked 11, etc. I recently read Greener's Modern Breechloaders where he says:

"All breech-loading barrels are fine-bored after they have received the proof-mark, in order to remove the indentations caused by stamping them at proof. It often happens that they are marked 13, and gauge full 12. Some American sportsmen will insist upon having their guns marked 12 at the proof. This is a great mistake. It is impossible for us to make a really first-class shooting gun
so marked. The same remarks apply to guns of 10-bore. These should be marked 11-bore, which allows the barrels to be, when finished, just under 10-bore."

Talking about shotguns, he explains that 13 just means a 12 sized gauge wouldn't slide down the barrel, not that it was exactly 13-bore. I'm following up to here.

My question is, regarding rifles and particularly damascus ones, was the preliminary proof done and the barrel size marked PRIOR to the rifling being cut?

It would still have to pass final proof anyway, and it would make sense to not invest the labor of rifling if the barrel was destined to fail due to a faulty weld anyway. In adition to the reasoning Greener states above, it could also explain the 13 marking on 12-bores if the barrel was 13 bore when initially proofed, but on the final product that was the land-to-land diameter. This is just idle curiousity on my part, but I've read through the 1868 act and some of the subsequent rules of proof without finding an answer. Thanks!
Bob