Lenny I went distingished with a M-1A and yes the 30 cal rules! I shot my M-1A barrel out and was given a 1-10 twist to replace it with. After one season with it, I replaced it with a 1-12 Keriger match contour. Little on the heavy side but I was steady in the wind. I found the 168 and 175s both loved the 1-12 twist. Buddy of mine turned me on to them but he owns a LARGE ammo factory in SD. I'm using Keriger 1-12 5R blanks for my first AR-10 builds. If I don't like them I'll go to Rock Creek Barrels. I've used thier barrels on some AR-15 builds and bolt gun builds. Us high power shooter are getting far and few between. Hold and X and pray for a 10. Rhino55