We always milled out a breech plug right on the barrel, after the barrel was finished. We would take a piece of round
stock, turn it down and thread it, and screw it in, or fit it to the barrel. I would then use the barrel to hold in the milliing
vise while I milled the plug out. After it was milled, we would take it out, file all the edges, then put it back in, file the top
and bottom and more or less clean it up. A lot of hand work, mostly filing, to do this, but it does make a good job....Don