rc20 said: "Shoot it 5 rounds, clean it, see how things look, shoot another 15"

this bbl was described in an auction listing as new unfired takeoff. 204 ruger. it looked unfired, and even looked like it had never been in a receiver. Anyway, i attached the chrono, laid it on the bags, fired a couple rounds from the hip (so to speak) and measured the fired formed brass. i am here typing so nothing went wrong. i headspaced it tight and sure enough the factory brass grew less than 0.001 on my starting loads (w748, speer tnt 39 gr, jump 0.030", new hornady brass, 3600 fps chrono'd).

QD'd the scope back on, and through the next 4 rounds adjusted down 12" and over 4" from my .308 zero. Shot numbers 7,8,9,10,11 went into 0.400", with 4 of them into 0.275. i had an idea what components to use since 748 and tnt's work great in my .223, but to be that lucky is about insane.

What is all this about break-in?