mont1120 Posted May 30, 2016 Share Posted May 30, 2016 At the local 3 Gun match yesterday, my DPMS M4 went south on me. It would fire about 15 rounds just fine, (30 round mags) then the next round would not feed, it just got jammed up on the lugs in the upper. I could clear the round, and not of the subsequent rounds would go into battery. I could smack the assist, and still no way it would lock up. I went to the safe area, but could not find anything in the barrel, I did try scraping off what looked like some small brass shavings, but nothing was visible. Went to the next stage, first 10 rounds went fine, locked up again. I tried it on one more stage after checking it again, and after about ten rounds, it was done. I tired my ammo in another M4, and they worked fine. I inspected the bolt head, the barrel itself, and just can't see the issue. Any ideas what I am looking for? There have been well over 10K rounds down the tube, but I do not think that is excessive. Link to comment Share on other sites More sharing options...
kurtm Posted May 30, 2016 Share Posted May 30, 2016 (edited) Reasons for this are many, here is what to check. Cracked cam pin. Cracked bolt tail where cam pin goes in. Jammed or broken ejector and or spring. Broken gas rings Primer anvil jammed in gas key.....not likely as it usually wont cycle. Cracked locking lug on bolt. Crap jammed under extractor, or bent extractor. Something in barrel extension. Something in throat of barrel. Edited May 30, 2016 by kurtm Link to comment Share on other sites More sharing options...
mont1120 Posted May 30, 2016 Author Share Posted May 30, 2016 Thanks Kurt, this is a good place to start looking for the solution. Link to comment Share on other sites More sharing options...
Bkreutz Posted May 30, 2016 Share Posted May 30, 2016 Since it consistently happens after 10 rounds, and returns to normal after cooling down (I'm assuming this from your description). I'd be looking for a crack on the bolt that is allowing the bolt to expand when it heats up preventing the bolt lugs to enter the barrel lugs. Link to comment Share on other sites More sharing options...
dauntedfuture Posted May 31, 2016 Share Posted May 31, 2016 Will the rifle go into battery without ammunition in it? If it does then there is always the possibility that ammunition is the problem. The fact that your ammo works in another rifle does not support this however, if the chamber on the other rifle is bigger then large ammunition would not work in your rifle. There is always the possibility of foreign matter in the rifle. I would also check the gas key and gas tube for evidence of damage. I don't think that a crack in the bolt would cause issues, but clean the bolt as well as you can then rub down with oil and wipe oil off. If there is a crack you will see oil seeping out. Many an AR has run without a lug on the bolt for some time until the owner noticed that a lug was missing. Link to comment Share on other sites More sharing options...
CJW Posted May 31, 2016 Share Posted May 31, 2016 I just had a similar issue, which turned out to be a cracked bolt at the cam pin hole. It started with some failures to feed, then a short while later turned into nothing feeding at all. Of course, this happened on the clock during a stage at a match... I dumped the rifle, took the missed target penalties and moved on, and when I finally back to the rifle the RO handed me the bolt head that had come completely apart inside the rifle. Link to comment Share on other sites More sharing options...
mont1120 Posted June 1, 2016 Author Share Posted June 1, 2016 It does happen with ammo. I too thought I might have issues with it, but I shot mine in another gun, and it was fine. I have checked the bolt, the face, barrel lugs, looked high and wide for junk, and find nothing wrong. Off to the range I go, completely mystified by this one. Link to comment Share on other sites More sharing options...
dauntedfuture Posted June 1, 2016 Share Posted June 1, 2016 Again, just because your ammunition works in another gun does not mean that there is not an issue with your ammunition. when you try to chamber the ammunition and it will not chamber, is the loaded round "stuck" in the chamber. If it is then its a classic case of brass not sized enough. Have you gauge checked your ammunition? Sometimes dies loosen up and your last few rounds could not have been sized all the way and they are sprinkled in with the good ammunition. If were talking just a hare out of battery then its most likely foreign material or undersized cases. Also consider, and I have seen this too, if your using mixed range pick up brass its possible your getting a mix of brass fired from a large chamber rifle. As your sizing die is not set to size enough, most of the brass is sized enough to work and these few odd cases that are way-big are causing a problem. Again, ammunition issue here. In many, many, many a case like this the first place to look is ammunition followed by magazines and lube. 90+% of rifle problems are caused by one of these three issues. Link to comment Share on other sites More sharing options...
jrswanson1 Posted June 1, 2016 Share Posted June 1, 2016 At the local 3 Gun match yesterday, my DPMS M4 went south on me. It would fire about 15 rounds just fine, (30 round mags) then the next round would not feed, it just got jammed up on the lugs in the upper. I could clear the round, and not of the subsequent rounds would go into battery. I could smack the assist, and still no way it would lock up. I went to the safe area, but could not find anything in the barrel, I did try scraping off what looked like some small brass shavings, but nothing was visible. Went to the next stage, first 10 rounds went fine, locked up again. I tried it on one more stage after checking it again, and after about ten rounds, it was done. I tired my ammo in another M4, and they worked fine. I inspected the bolt head, the barrel itself, and just can't see the issue. Any ideas what I am looking for? There have been well over 10K rounds down the tube, but I do not think that is excessive. The part in bold is your problem. Link to comment Share on other sites More sharing options...
kurtm Posted June 1, 2016 Share Posted June 1, 2016 Wow, did you just show up from ARFCOM??? Link to comment Share on other sites More sharing options...
12Bravo Posted June 1, 2016 Share Posted June 1, 2016 Was waiting for someone to take a shot at DPMS... Link to comment Share on other sites More sharing options...
Stlhead Posted June 1, 2016 Share Posted June 1, 2016 My magic 8 Ball says it is a problem with your bolt. 10,000 is a good run for a bolt, pop in a new one and see if that fixes your problem. Link to comment Share on other sites More sharing options...
Stlhead Posted June 1, 2016 Share Posted June 1, 2016 Someone post "the chart"! Link to comment Share on other sites More sharing options...
mont1120 Posted June 2, 2016 Author Share Posted June 2, 2016 Picking up bolt today, buying a box of factory rounds, then headed for the range. Never heard anything bad about DPMS. I suppose I just opened a door for those who dont like them. Have there been problems I am unaware of with the platform. Link to comment Share on other sites More sharing options...
jrswanson1 Posted June 2, 2016 Share Posted June 2, 2016 Picking up bolt today, buying a box of factory rounds, then headed for the range. Never heard anything bad about DPMS. I suppose I just opened a door for those who dont like them. Have there been problems I am unaware of with the platform. Did you pick up a new bolt or are you using the original one? Link to comment Share on other sites More sharing options...
mont1120 Posted June 3, 2016 Author Share Posted June 3, 2016 New, I have already broken my first bolt a few years ago, it did break a lug off at a match. DPMS replaced it for no charge. Link to comment Share on other sites More sharing options...
mveto Posted June 3, 2016 Share Posted June 3, 2016 I had a similar issue with a bolt a few months ago, along with it failing to fully go into battery it also would fail to eject spent cases, the cases would be literally stuck to the bolt face. I checked several things including the ejector spring and extractor, and they were all fine, replaced them with known working parts and it still would happen. It ended up that the inner diameter of the bolt face was slightly undersized. It was cut at .374 while SAAMI specs for the rim are .378. When I had brass that had a rim of around .376 the cases would get stuck and it was hard to even force them onto the bolt face by hand. This was causing both the failure to go into full battery and the failure to eject the spent round. Rubber City was great about it all and I sent them the entire BCG and they replaced the bolt and since then I have had zero issues with several hundred rounds down range with it. Before it was happening at least once on every mag. None of the previous problems have come back. Link to comment Share on other sites More sharing options...
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