I watched a retired gunsmith who had been a barrel fitter long ago, who had fit barrels for Fox, back when they were still in Philadelphia. He was fitting two sets of barrels to a gun which had been recase colored. One set I think was from the gun and the second was new to the gun. He was one of the old school, measure several times and cut once, type of craftsman who could almost feel the adjustments as much as see or explain them.
Lamp black, files, small hard stones, fine emory paper and a hammer were used. He said that the frame had warped slightly in the coloring. He set the reciever on a thick leather pad and stuck it smartly with a lead faced hammer. My eyes got real wide at that point. Checked the fit and repeated the hammering again. Then he went to work with the files and later the small polishing stones. Entire process took half an hour for the first set of barrels.
Then he fit the second set by only adjusting the second set of barrels. No more adjustments were made to the reciever. Last he fit the one fore end to the second set of barrels. He told me that often it was far easier to get each barrel to fit a seperate fore end than try to use the same for both. Sometimes the second barrels would not fit very well to the one fore end and he said that he "had to split the difference". The man was so fast that it made me understand just how little most of the "gunsmiths" that I knew realy knew. More theory than fact and more theoritical than experience.
Other than striking the reciever, with a hammer, I have used most of the tricks that I saw him do that day in fitting barrels. Just wish I had a chance to work with him a few days. I am sure he could have shown me tons more if I had only asked. I regret that I can not remember his name. Sad, I can see his face and remember he had kind of a hissing whistle as he let air out between his teeth. Some little diddy that he use to whistle. I was very young in those days and he seemed older than dirt to me. In fact he had to be past 70 or 75 at the time and that was over 40 years ago. I guess that makes me close to older than dirt myself.