greydog,
I have seen the results of some of the problems you mention through my borescope more than once.
A number of years ago a friend had a Remington 700 Classic in .250 Savage that shot extremely well. A gunsmith friend told him it would work much better if rechambered to .250 AI, and guess what? The gunsmith had a .250 AI reamer.
Eventually my friend caved and let the gunsmith do the job, which included setting the barrel back a couple threads to totally clean up the old chamber. The rifle never shot worth a darn again. I would guess the factory chamber job was well-done, because the rifle shot so well, but do know the rechamber wasn't, because I got to look at it through my bore-scope: The rifling was obviously much longer on one side of the throat than the other. (I reported this off-center rechamber job in an article years ago, and the magazine got a nasty letter from a reader, saying it was impossible for a chamber to be off-center, due to the pilot on the reamer.)
But have also seen the same thing, a number of times, in the throats of various factory rifles. The really interesting part is sometimes they still shoot pretty well!
