I've been reading as much as I can on this, and one point that is seldom mentioned bbl. break in regarding X Cal. Bbl's or other $$$ barrels that cause copper build up is the chambering where there are microscopic scratch's left in the leade by the reamer.
That being said, I have a 22 BR chambered by Apache and a 6 6BR chambered by X Cal.
So. ALL you X Cal. barrel owners,Tell me your break in procedure ??