Quote Originally Posted by Cdexter87 View Post
Loaded up my few rounds last night under sammie according to book but wouldn't chamber in ar10.

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Well I load for an AR-10. Have been for years. My guess and this is just a guess (your head space is off). I take it the bolt is NOT closing all the way? In which case you need to screw your sizing die down more. Your head space is measured from the datum line (that's where the shoulder starts on the neck to the bolt face. If that shoulder is not pushed back that bolt will not close. I shoot 150 gr fmjbt & 168 gr Nosler Competition with no problems.