I think barrels break in as you shoot them. Depending on the barrel they improve after maybe 50 to 100 times. After some 1,000’s shooting they start shooting worse, the number of rounds depend largely on a couple things. But I think the heat & number of rounds.
As far as breaking in procedure I don’t have an opinion on whether or not a particular procedure helps.

I prefer classic.
Semper Fi
I used to run with the hare. Now I'm envious of the tortoise and I do my own stunts but rarely intentionally