Re: converting a .30-.378 to a .338-.378
Any good barrel company is the way to go.(Hart,Lilja,Rock, Krieger, Lawton, PacNor) Stay with a 10 twist as your prolly going to be shooting the 300gr or heavier bullets. 28" is fine, depending on what your going to use the rifle for, carry, longrange, ect. I have built many of them with 26" bbls+brake for carry rifles on elk hunts. You can expect around 2900fps with a 26" bbl with the 300grn pill. Longer bbl will get you into the 3000 range.