Met an old timer months ago with a new AR-15 Blackout at the shooting range. He was constantly struggling with misfires and bolt jambs. He is the guy that introduce me to these bolt free tools.
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Bumped into the guy several times. I told him it appears something is wrong with the firing chamber. The bolt would fail to close by at least 1/8". He finally returned the upper receiver to the manufacturer and they replaced the barrel. Met the guy today and he is struggling with his stuck bolt again. He said the new barrel didn't change anything. We tried one of my plastic magazines in this gun and no change. I got to thinking I had my AR 223 with me so we installed my lower receiver under his 300 aac upper and his bolt. Significant improvement, I thought we had it then after 6-8 rounds it jammed again. Next we tried my bolt and my receiver under his upper, no change. We did determine the bullet does properly seat in the firing chamber. The bolt itself is sticking. Actually the bolt fails to close. I tinkered with the charge handle, opening and closing the bolt, eventually the bolt will go closed and fire properly but chances are it will fail to cycle.
My theory is the upper receiver has issues. Is there any chance the bolt is not concentric with the barrel or is it something else? The bolt has those gear teeth that mesh with gear teeth in the barrel. I think the problem is right there. I recall the barrel had an indexing pin that engaged with a slot in the receiver,
wonder if the slot is not properly indexed, or the slot that indexes the bolt.
opinions and theories welcome
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