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Posted: 2/5/2009 7:59:48 PM EDT
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Ok, anyone got any ideas here? I just sheared off two locking lugs on each side of the extractor.
Here's the story, DPMS upper, full size, fired about 800-900 rounds, gun was a little dry but was functioning 100%. Was actually running magazine tests. In middle of a 20 round magazine, the riflejams, a live round about 3/4 in the chamber. We pull bolt to rear and lock it in place, blot moves freely. Lightly tap buttstock on bench and round slips out of chamber and falls out of ejection port, along with what i think is a piece of plastic. We look closer and see its metal, (puzzled look for a few seconds and lightbulb goes off) So boly forward break it open and pull bolt out and see that 2 lugs on each side of extractor are gone. We find three pieces total on the ground and bench. Three of four sheared areas are shiney, like they just came off. One is "dirty". Check the chamber (with light) and find no damage to breach face of lugs on barrel. THe entir rifle looks fine except for the bolt, which stuill goes in and out just fine. Looking at the broken off parts, it looks like there are shear marks along the lugs, not across them. Anyone have any idea what the heck? I took pictures bu to fuzzy, so I might take more if anyone thinks a visual might help. Oh, rifle has maybe 2000 rounds through it, all factory |
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Locking lugs on either side of the extractor take more stress than the other ones and tend to fail fist.
I agree that it's weird that it would fail at such a low round count. You're not doing anything like oiling or greasing the cartridges are you? Was headspace ever checked on this rifle? BSW |
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Quoted:
Ok, anyone got any ideas here? I just sheared off two locking lugs on each side of the extractor. Yep. DPMS
Read: http://www.ar15.com/forums/topic.html?b=3&f=118&t=413742&page=1 http://www.ar15.com/forums/topic.html?b=1&f=5&t=795573 |
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Sorry guy, you got suckered into buying a DPMS. Crappy bolts.
But what the heck, now you have a reason to get a good one, if you can find it. Some decent bolts come up on the EE every couple days or so. Get a Colt, BCM or LMT bolt and then get back to shooting. And don't believe those schmucks who tell you "you don't need an MP HPT bolt." Nonsense. Of course you do. And now you know why. |
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Magnetic Particle testing is not going to tell you if the part was heat treated too deep, making the part too brittle and caused the lugs to shear. It will just tell you if the part is cracked to begin with.
Even Colt/FN has bad batches from time to time. Again, get DPMS on the phone, and they will replace the bolt for free (with one from a batch that does not have problems). |
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Quoted:
Magnetic Particle testing is not going to tell you if the part was heat treated too deep, making the part too brittle and caused the lugs to shear. It will just tell you if the part is cracked to begin with. Even Colt/FN has bad batches from time to time. Again, get DPMS on the phone, and they will replace the bolt for free (with one from a batch that does not have problems). No manufacturer is 100%. Having said that, I'll take the ones who actually bother to test their stuff over those who don't. It's not like DPMS has a great rep and the occasional screw up. But your mileage may vary. If you're just shooting at the range, a broken bolt isn't the worst thing in the world, as long as you have a spare. |
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