I believe the current twist rates for either caliber, is 1-18.7. If you can find an old 10'' from Palmer,Ma. they had a 1-14 twist.(I have one, and it shoots the heavier 180-200gr bullets real good.) I know a few years ago they we're talking about coming out with some 1-16'' twist barrels, but I could never find out if they did or not. gypsyman