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Posted: 3/21/2014 5:06:48 AM EDT
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I purchased a Del-Ton complete upper in M4 configuration. Spikes lower. PMags.
I shot it for the first time yesterday and had two malfunctions. It appears the bolt did not completely pick up a round and the bolt lugs caught the round midway, bending the case. In the pics below you can see where the bolt lugs drove into the case. The projectile itself has scratches which look like it may have contacted the edges of the feed ramps. My question is, has anyone had a burr on their feed ramps that caused this problem? Do, in some cases, the feed ramps need to be polished? Bolt marks 
Bent case 
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Quoted:
I just broke it down. Looks exactly like the upper right pic. Could a burr on the ramps cause the problem? It appears like there is a minute amount of copper being shaved off the projectile. is there any sort of lip at the bottom edge of the extension (shiny part above) where it meets the receiver (black part above)? you can use the end of a wooden Qtip or some such and run it over that area; it should feel pretty smooth. is the alignment of the ramps good? note that if you go at that area with a file, the barrel extension is hard 4150 ordnance steel, and the upper receiver is aluminum, so the aluminum is going to disappear a lot faster than the steel. ar-jedi |
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Quoted:
is there any sort of lip at the bottom edge of the extension (shiny part above) where it meets the receiver (black part above)? you can use the end of a wooden Qtip or some such and run it over that area; it should feel pretty smooth. is the alignment of the ramps good? note that if you go at that area with a file, the barrel extension is hard 4150 ordnance steel, and the upper receiver is aluminum, so the aluminum is going to disappear a lot faster than the steel. ar-jedi Quoted:
Quoted:
I just broke it down. Looks exactly like the upper right pic. Could a burr on the ramps cause the problem? It appears like there is a minute amount of copper being shaved off the projectile. is there any sort of lip at the bottom edge of the extension (shiny part above) where it meets the receiver (black part above)? you can use the end of a wooden Qtip or some such and run it over that area; it should feel pretty smooth. is the alignment of the ramps good? note that if you go at that area with a file, the barrel extension is hard 4150 ordnance steel, and the upper receiver is aluminum, so the aluminum is going to disappear a lot faster than the steel. ar-jedi Alignment is good to go. I'll try the Q-tip and see if any burrs are present. If there are any burrs, I have a diamond rod about the same diameter, and will use that instead of a file. |
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New weapons tend to be tight until broken in. I have seen similar in new weapons that have not been lubed sufficiently. I expect it needs to be broken in. I'm running it wet. I'll give it a couple hundred rds. and see if things improve after checking for burrs. |
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Problem is a bolt over rim on the feed (bolt pushing the round out of the mag via the middle of the case, not the back of the rim) and the problem is either a short stroke, or the mag not recovering fast enough/correctly to get the top round in the mag tight up against the bottom of the mag feed lip.
Start trouble shooting by loading only a singe round in a mag, charge and fire the single round with the empty mag still in the rifle, and see if the bolt locks back (bolt catch holding the bolt back via the catch in front of the bolt face, and not just the catch on the bottom of the carrier. If the bolt locks back via the single round fire test, then it a mag problem, so start off by pulling the mag down and CLP cleaning it. Next, take a look at the threads part of the mag catch, and make sure that it flush with the face of the mag release button. If you still have problems, then need to know that mag type since if it a 10 rounder, could be a problem with the mag feed lips, or even incorrect tension of the spring to the bottom of the follower to get the top round fully against the mag lips on recovery. |
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I'll try what you suggested in the morning. Close neighbors work @ night and sleep days. I shoot in the backyard, so no waiting to hit the range.
Everything is new, gun and mags. Even though the mags are new, it doesn't mean they are not dirty or debris from manufacturing. |
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Quoted:
I'll try what you suggested in the morning. Close neighbors work @ night and sleep days. I shoot in the backyard, so no waiting to hit the range. Everything is new, gun and mags. Even though the mags are new, it doesn't mean they are not dirty or debris from manufacturing. Also, make sure that you correctly clean (including a chamber brush with CLP to scrub the chamber), and correctly lube the rifle before you shoot it again. The lack of correctly cleaning to get out the assembly/storage grease, and lubing the upper bearing areas before the rifle is fired can cause a great deal of problems. |
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I just finished ck'ing and cleaning mags. (Magpul GEN M3 Window)
There seems to be a lot of forward/rearward movement with the mags in the magwell. I've had several ARs and I used GI aluminum mags, but don't remember there being that much play.(sloppy) As much as it moves, I'm thinking it may be causing the bolt to not properly strip a round from the mag. Has anyone else experienced this play? |
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Quoted:
I just finished ck'ing and cleaning mags. (Magpul GEN M3 Window) There seems to be a lot of forward/rearward movement with the mags in the magwell. I've had several ARs and I used GI aluminum mags, but don't remember there being that much play.(sloppy) As much as it moves, I'm thinking it may be causing the bolt to not properly strip a round from the mag. Has anyone else experienced this play? Make sure that the threaded section of the mag catch assembly is flush with the face of the mag release button. If the catch needs to be threaded more into the mag catch button, then push the mag catch button in all the way (which will push the catch assembly on the other side clear of it channel), then thread the catch the needed amount more. If you find that the catch is either a half thread in, or a half thread proud of the face of the button, then thread the catch all the way out of the button, and turn the button 180* in the channel for it so the threaded section will now thread flush with the face of the button. |
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The catch is flush.
Excuse my ignorance, but does moving the catch in or out, tighten the mag in the well? I tried a 10 rd. PMag, and it is tight in the magwell. I hand charged all 10 rds with no problem. Did the same with the three 30rd mags. If the mags are pushed forward, the bolt would pick up the rounds 1/4 way up the case instead of the rim. When the mag was pulled rearward, there were no misfeeds. |
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I noticed the rounds that I hand charged were being engraved by the ramps, even though the Q-tip test did not indicate any burrs.
I took the diamond impregnated rod and ran it over the two ramps but stayed off the receiver portion. I loaded a 30 rd. mag with new rounds and hand charged the complete mag. No mis-feeds or engraving of the projectile or case. Now time to wake the late sleeping neighbors :-) and test fire. |
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Quoted:
The catch is flush. Excuse my ignorance, but does moving the catch in or out, tighten the mag in the well? I tried a 10 rd. PMag, and it is tight in the magwell. I hand charged all 10 rds with no problem. Did the same with the three 30rd mags. If the mags are pushed forward, the bolt would pick up the rounds 1/4 way up the case instead of the rim. When the mag was pulled rearward, there were no misfeeds. How much does the 30 round mags rock/cant in the mag well now. The mag catch should pretty much lock the mag high enough in the well (if the both the catch and the mag are machined correctly) so you don't have such problems. If you are able to push the bottom of the 30 round mag's forward, and it allows the bolt to miss the back rim of the top round to grab the round at the middle of the case, then this is your problem. When all else fails, try some aluminum USGI 30 round mags to see if they have the same problem (weed out if it's the mags, or the lower receiver/mag catch that is out of spec instead). |
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It could be a mag catch hole drilled incorrectly on the receiver. If it is to low, you would get the case issue in your photos. First try another mag or two that are different. Use an aluminum GI 20 rounder etc. just nothing that is similar to what you have been testing. If same thing happens, my guess is receiver hole for the mag catch is out of spec. If this fixes problem, then you have a mag problem. I don't think it would be a short stroke problem because if it was, usually the round is not stripped off the magazine or you get a failure to eject problem.
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I had a chance to test the NHMTG mag this morning. Loaded 30 rds. and had two failure to loads like the PMags. It occurred on the 2nd and 5th round. After clearing the 5th rd., there were no more failures.
I then loaded a PMag and had no failures. I again loaded the NHMTG mag w/ 30 rds. No failures. I'm assuming the rifle needs a good breaking in. Thanks all who helped with this issue. |
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http://www.ar15.com/forums/t_3_66/629787_.html&page=1
Lots of people think this is bolt over base. I disagree and that round looks IDENTICAL to the issue I was having. NOT bolt over base. |
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