I agree Alex. There can be a lot more harm done than good with that method if not careful. It's pretty hard to accurately test anything if you don't know what it is when done.. I want no circular machining marks on the leade angle and no burrs, without changing anything dimensionally. If it's good to start with it's a lot easier. Although a different set of challenges boring does that for me. Certain types of rifling helps too.
I hear what you’re saying but I can assure you at least 2 of the best rimfire smith known do it this way. I know this because I learned from them. You’re not lapping enough to cause any of the issues you speak of. Or at least you shouldn’t if you’re using a sound chambering process.
A friend who does his own work built himself a really good shooting .22 RF bench rifle and has shot is quite a lot, doing very well. A couple of times he started loosing a point or two that he did not think came from misreading his flags, or his shooting. Upon further inspection he determined that there was a minuscule deformation of the corner of a land, at the crown, that he thought probably happened when he pulled a brush back into the barrel. Both times recrowning fixed the problem, so for his rimfires, he now unscrews the brush instead of drawing it back into the barrel at the muzzle. He has never seen this problem with his CF bench guns and attributes that to the more robust nature of jacketed bullets. He has a couple of really fine 6PPCs that he shoots in competition, and practices a lot with.
