Relieving hidden stresses in barrel steel in the course of machining same is a very real phenomenon. I experimented once with a pristine military Mauser barrel. It was scary accurate in its original configuration- steps and all. I carefully set it up in a 4-jaw chuck, tailstock live center carefully centered and supporting the muzzle end. On slow speed I painstakingly turned the barrel into a svelte taper, eradicating the steps. A work of art when done. Subsequent shooting proved the first shot would go dead nuts where the crosshairs pointed. Second, third, fourth, fifth shots would steadily walk up and to the right with the fifth landing about 8" from the first, every time. I messed with the bedding every which way from Wednesday and nothing helped. Stress relief is a bitch.
Thorough cooling between shots would yield MOA groups but I couldn't live with knowing it's foible, so away it went. I did kill a couple deer with it.
