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Posted: 8/23/2012 10:55:32 PM EDT
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I got a 7.5" x39 barrel a while back...
Shot fine, no problems, even quite a few sessions of bumpfiring.... When I built it, checked headspace and it was fine. After about a thousand rounds, I broke a bolt....... Got a replacement under warranty... Guy said the headspace was off..... I didn't believe him, figured it was just BS to make me think it was a weapon problem instead of a 'their bolt' problem. Well, I got about 10 rounds and.........the new bolt went TU as well.. So... Can a barrel with only about 1K rounds through it, have changes in headspace? Can a bolt BREAK because of a headspace change? IIRC, he said it was 7 thousandths out of spec, or maybe it was supposed be 3 thousandths and it was 7 thousandths, can't remember........Anyway, he said it was out of spec. I know x39 bolts break, and even the superalloy bolts aren't rated for 7.5" barrels, but some people run them no problem. So, I can either BUY a 7.5" barrel and hope I don't keep chewing through bolts, or get a 10.5" x39 barrel and drop the chamber pressure by 10K PSI.... Which should help with dwell time and unlock, meaning less stress on the bolt lugs...... Thoughts? Answers? BOTH times that the lug broke, I was bumpfiring, FYI. |
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Headspace is determined by the combination of how the chamber is cut referenced to the barrel extension, and how the bolt is made. Changing bolts, changes the headspace. If headspace with the new bolt is off, then it's off. Try a different bolt. If you find multiple bolts showing incorrect headspace in the same way, then would suspect a barrel not chambered correctly.
7.62x39 case head diameter leaves very little support for the locking lugs on an AR15 bolt, and very short gas system configurations tend to be more stressful on bolts, so you have a problematic combination. |
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These bolts were designed to mitigate the bolt thrust and other issues with 7.62 x 39 and 6.5G and other type bolts in that class.
They have taken care of a lot of guys problems. Good stuff. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDMQFjAC&url=http%3A%2F%2Fwww.ar15performance.com%2Fnew_products&ei=2zA3UN7RHqHr6wHyqIGICQ&usg=AFQjCNHVOavdGZoudE0t48sa77v9p3fYxg&cad=rja Lot's of recommendations on the 6.5G forums as well. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&ved=0CHMQFjAJ&url=http%3A%2F%2Fwww.65grendel.com%2Fforum%2Farchive%2Findex.php%2Ft-2167.html&ei=2zA3UN7RHqHr6wHyqIGICQ&usg=AFQjCNEE3GFVBWhYH-6d7dfxGvDhPmDDYQ |
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