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Posted: 7/19/2016 10:20:52 PM EDT
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Hey all, I'm new to the AR-10 world. I bought a built upper and had a local Class III guy build me a lower. Well, the initial shots did not go well. Extreme back pressure resulted in blowing out PMAG and the brass casing getting blown up. The back part, including primer was ejected, but the middle portion, from the back ejected portion to just short of the part of brass that necks down on a .308 was still lodged in barrel and mangled behind feed ramps. Once that was removed, the rest of the brass, including the necked down portion was still lodged in barrel. A properly sized screw driver wedged in was able to remove it rather easily.
Same thing happened on the next test shot after re-assembling upper. Feels almost as if the barrel is not proper caliber although it clearly states DPMS 308 1-10 on it. These shots have resulted in some damage to upper receiver inside along top edges near charging handle channel. Also some fresh damage on threads on lower receiver where bolt carrier group comes back into buffer tube. At this point I'm lost and could use some insight where to test or what may be defective. Any help is appreciated. |
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Who did you but the upper from?
Any info on bcg? Mfg of upper receiver? Mfg of lower? You need to measure your buffer, buffer spring, and count the coils. You need to measure your buffer tube length. Report back with ammo mfg and type. Previously mentioned measurements. And pictures of the damage as clear as you can. If what you're describing is what I'm imagining, your upper is toast. DO NOT SHOOT IT AGAIN UNDER ANY CIRCUMSTANCES UNTIL YOU REPORT BACK WITH PROVIDED INFO AND PICTURES. You could've fractured the upper, and it's beyond repair. If you try shooting it again, you can have shrapnel if your face. |
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I'll get pictures this afternoon after work.
I hadn't planned on shooting it. Haha. The upper was an Aero Precision, CmmG lower, Luth stock, DPMS bull barrel, first ammo was Federal heavy grain, second was match grade reload my Class III buddy had. The buffer is a heavy duty, but I'm not sure about the spring. The upper is toast, the lower seems to be fine. The upper was bought at a gun show but was checked out by my FFL Class III builder. Like I said, I'll get pictures later. Thanks for yalls help. |
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I'll get pictures this afternoon after work. I hadn't planned on shooting it. Haha. The upper was an Aero Precision, CmmG lower, Luth stock, DPMS bull barrel, first ammo was Federal heavy grain, second was match grade reload my Class III buddy had. The buffer is a heavy duty, but I'm not sure about the spring. The upper is toast, the lower seems to be fine. The upper was bought at a gun show but was checked out by my FFL Class III builder. Like I said, I'll get pictures later. Thanks for yalls help. Where both the blowup so with this? |
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The short buffer will cause the damage to the lower receiver threads. Also if that is a carbine length spring it might be just enough to cause an early unlock of the bolt. Quoted:
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Would that cause this problem? The short buffer will cause the damage to the lower receiver threads. Also if that is a carbine length spring it might be just enough to cause an early unlock of the bolt. But the failure resulting in the rounds being shredded? Would the buffer/spring combo result in anything like that. |
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It's. Luth stock, the buffer tube and set up is for a .308 carbine.
Gas tube length is 9.5", that's equal to a mid-length system. Since the barrel is a DPMS .308, I assume it's using standard AR-15 gas length systems. So, is the carbine buffer and tube assembly too short to operate correctly? The lower is a CMMG not sure if it was built to Armalite or DPMS specs, but I don't believe this is a problem, is it? |
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I'll get pictures this afternoon after work. I hadn't planned on shooting it. Haha. The upper was an Aero Precision, CmmG lower, Luth stock, DPMS bull barrel, first ammo was Federal heavy grain, second was match grade reload my Class III buddy had. The buffer is a heavy duty, but I'm not sure about the spring. The upper is toast, the lower seems to be fine. The upper was bought at a gun show but was checked out by my FFL Class III builder. Like I said, I'll get pictures later. Thanks for yalls help. You need a buffer like this. Your rifle is dpms pattern if one was ar10 they wouldn't fit together correctly. i think the buffer may be your problem causing premature unlock as others have suggested. |
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Also if you don't want that upper I'll take it. May be salvageable Why risk it? It's already been through 2 what seem to be OOB discharged. Just because fracturing isn't visible, doesn't mean it didn't happen. Looking at the cam path, it looks pretty mangled. Lots of malfunctions will come from that. Scrap the upper. Murphys law and all that. From the way the case looks, OOB makes sense. Or, possibly a crazy occurrence of having carbine buffer in rifle tube. I haven't seen that happen before, and would be strange to do it twice. Or, the barrel was installed wrong? I've read of people putting shims on the barrel nut. What would happen if they put the shims on the barrel flange by mistake? I've never encountered this, and imagine it would not fire. What handguard was on it? |
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I'll get pictures this afternoon after work. I hadn't planned on shooting it. Haha. The upper was an Aero Precision, CmmG lower, Luth stock, DPMS bull barrel, first ammo was Federal heavy grain, second was match grade reload my Class III buddy had. The buffer is a heavy duty, but I'm not sure about the spring. The upper is toast, the lower seems to be fine. The upper was bought at a gun show but was checked out by my FFL Class III builder. Like I said, I'll get pictures later. Thanks for yalls help. I would take it to a different gunsmith, and have them check the headspace. The only catastrophic failures I've seen of that nature are overloaded ammo, and incorrect headspace. |
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I would take it to a different gunsmith, and have them check the headspace. The only catastrophic failures I've seen of that nature are overloaded ammo, and incorrect headspace. Quoted:
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I'll get pictures this afternoon after work. I hadn't planned on shooting it. Haha. The upper was an Aero Precision, CmmG lower, Luth stock, DPMS bull barrel, first ammo was Federal heavy grain, second was match grade reload my Class III buddy had. The buffer is a heavy duty, but I'm not sure about the spring. The upper is toast, the lower seems to be fine. The upper was bought at a gun show but was checked out by my FFL Class III builder. Like I said, I'll get pictures later. Thanks for yalls help. I would take it to a different gunsmith, and have them check the headspace. The only catastrophic failures I've seen of that nature are overloaded ammo, and incorrect headspace. I just can't see the wrong style buffer causing this major of a failure all on it's own. Unless both the reloaded and factory ammo were overloaded headspace is what I would think caused this type of OOB failure. |
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I just can't see the wrong style buffer causing this major of a failure all on it's own. Unless both the reloaded and factory ammo were overloaded headspace is what I would think caused this type of OOB failure. Quoted:
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I'll get pictures this afternoon after work. I hadn't planned on shooting it. Haha. The upper was an Aero Precision, CmmG lower, Luth stock, DPMS bull barrel, first ammo was Federal heavy grain, second was match grade reload my Class III buddy had. The buffer is a heavy duty, but I'm not sure about the spring. The upper is toast, the lower seems to be fine. The upper was bought at a gun show but was checked out by my FFL Class III builder. Like I said, I'll get pictures later. Thanks for yalls help. I would take it to a different gunsmith, and have them check the headspace. The only catastrophic failures I've seen of that nature are overloaded ammo, and incorrect headspace. I just can't see the wrong style buffer causing this major of a failure all on it's own. Unless both the reloaded and factory ammo were overloaded headspace is what I would think caused this type of OOB failure. I reload, but I've never had a kaboom of any kind. The pic of the separated cartridge looks more like what I'd "expect" an explosion to look like rather than a "tearing" of the cartridge due to early unlocking. Am I wrong in my observation?...again, limited personal experience with "kabooms". One thing the OP said in his initial post that concerned me was the description of the ammo. I think I would have given a very exact description of the "heavy" Federal bullet fired first, and of course the description of the other bullet being a "match reload". I'm also wondering about the primer being ejected. Would this be likely due to an early unlock event?...or overpressure in the case? |
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My first thoughts are:
1. Mismatched bolt and barrel extension, one is the DPMS style and the other is Armalite's. 2. Gross excessive or insufficient headspace. Your gunsmith failed to check it with "Go" and "No-Go" gages or he would have discovered it immediately. 3. Bad ammo, really bad ammo. Who's ammo was the "heavy" stuff you fired first? Heavy as in bullet weight or heavy as in powder charge? If both were your "Class III" gunsmith's doing he owes you a new upper including the barrel, bolt, bolt carrier, charging handle and receiver. He built it and his ammo broke it or he never checked headspace and either one of his two failures caused the catastrophic failure. Two shots fired and two KaBooms, what are the odds of that. If HE wants to shoot it again, make sure you're as far away from him and the firearm as you can get. The buffer has zero effect on guns blowing up or not. |
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I don't think the bolt could be an issue. I have NEVER heard of a kaboom coming from an Armalite bolt on dpms extension, or vice versa. Just failure to fires. I just don't see that happening, but just because i haven't seen it, doesn't mean it hasn't happened.
From looking at the case, extremely bad head spacing makes sense. That's why i started thinking maybe they put shims in front of the barrel extension flange instead of on the nut side. I've never seen this happen before, and am trying to imagine what would happen. We need more info and pictures. But, if your "3rd class" gunsmith did this, he's at fault and should replace everything. |
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Yeah...maybe I missed info on the ammo but all I see is a headstamp. Was the ammo reloaded? Factory from the same lot?
It looks like it is softpoint which means reloaded....someone screwed up... Notice the flattened nose on that round? Either it has been chambered or it smacked the hell out of the front of the magazine during recoil... |
| Being a little new to trying to diagnose a kaboom, I have a question. In the pic of the damaged case, is the first separation in the case up by the bottleneck a "tear", and the second separation toward the head an explosion separation? The bottleneck/front area looks like the separation occurred while that part of the bullet was still retained in the chamber. The lower/case area separation with the curled brass looks like that part of the bullet was out of the chamber at the time of powder ignition. These are my lay observations, and I'd like to hear from some with more knowledge and experience in this area. |
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Being a little new to trying to diagnose a kaboom, I have a question. In the pic of the damaged case, is the first separation in the case up by the bottleneck a "tear", and the second separation toward the head an explosion separation? The bottleneck/front area looks like the separation occurred while that part of the bullet was still retained in the chamber. The lower/case area separation with the curled brass looks like that part of the bullet was out of the chamber at the time of powder ignition. These are my lay observations, and I'd like to hear from some with more knowledge and experience in this area. The forward separation is almost a classic example of a casing that has been loaded too many times and become thin and brittle, thus breaking off in the chamber when fired. This is exacerbated by excessive headspace. Which... Is nearly always the cause of the catastrophic case head failure of the rear portion. |
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I'm not sure, but I didn't see any shims when we removed the barrel. I'm not sure about barrel extensions or how to check that
By heavy Federal, Federal makes at least two types of .308 ammo that were at the store. I purchased the heavy or higher grain Federal ammo. That is the round I posted a picture of. The second shot was a reload my dealer had. We didn't recover that casing. Walked off and when return to find it, we couldn't locate in the brush. |
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I'm not sure, but I didn't see any shims when we removed the barrel. I'm not sure about barrel extensions or how to check that By heavy Federal, Federal makes at least two types of .308 ammo that were at the store. I purchased the heavy or higher grain Federal ammo. That is the round I posted a picture of. The second shot was a reload my dealer had. We didn't recover that casing. Walked off and when return to find it, we couldn't locate in the brush. Federal Fusion? |
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