I have a .223 and had a .20vt chambered by Devin at Sinn Arms, both blanks from McGowen. Both shooting groups like Jamie , this .223 does it with 55-82 grain bullets in 8 twist. So I agree it matters who does the cambering. And Devin does great work! (please don't order any until he finishes my .221fb). And my rifles aren't anything special, factory hunting stocks and actions. The .223 cleans good, probably one of the easiest I've broken in yet. The .20vt was a bit fussy, but I think it was my choice of ball powder.