Should I mention the practice of setting the barrel up on an actual cartridge or case?
Naw, let's don't, it would take a long thread to explain why that won't work, even though it does; especially if you have a case of brass of the same lot, enough to wear the barrel out.
Jim Watson, should you mention? You are preaching to the choir, Roy Dunlop said he preferred to purchase gages. He claimed he had friends that did not purchase gages and he said there was nothing suspect about their work. Today reloaders have their favorite/go to source for gages and no one can compare with their accuracy. I am not that vain,
I have confidence in my ability to measure the length of a chamber, length of the case from the shoulder to the case head. Again, I purchased a mill from a military recourse type on the M1, 03, 03A3, 1911 etc. He was having a difficult time determining the length of a chamber for a Rock Island 03 period correct 1911. He had 20 30/06 head space gages of different length. but nothing fit. He was on a forum that with a choir that wanted to pick them. And then as always they went after each other and left him with no way to measure the length of his chamber 'for clearance'.
I paid him for the mill, we loaded it and then I offered to help him; I gave him 4 choices. The easiest and most simple method indicated his chamber was .0075" longer than a minimum length/full length sized case or .0025" longer than a go-gage length chamber. It was then he decided he wanted the chamber to be go-gage length.
(Again) He had 100+ 03 type bolts, none of the bolts would reduce the length of the chamber .0025". I have 25+ 03 type replacement bolts, none of my bolts would reduce the length of his chamber.
I offered to size cases that would off set the .0025", he wanted the new owner to be able to purchase new, factory, over the counter ammo so that left him with finding a bolt that shortened the length of the chamber .0025".
The best advise he could manage from the Internet was the suggestion one member offered; purchases a bucket of bolts. And then I suggested if he knew out to measure a bolt and the supplier knew what he was doing he could get the correct bolt the first time.
I offered to measure the effect each bolt had on head space, all 100+, and then think about all the experience he would gain; he was not interested. He did contact another resource type. The other resource type sent him 5 more bolts.
F. Guffey