Posted: 9/8/2013 6:42:42 AM EDT
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I'm looking for some opinions on an issue I experienced yesterday at the range. I took out my new Colt LE6920 to sight it in and funcion test. I was shooting gen2 30rd PMAGS. Initially everything functioned fine but after about 20 rounds into my session the bolt stopped locking back on last round. I tested all three mags and they all experienced the same thing but it was intermitant. I then adjusted the stock to give me a better/tighter hold on the rifle and after that everything worked fine. Bolt locked back normal etc.
So my question, would or can the grip/hold on the rifle have any affect on the ability of the bolt not locking backor cycliing correctly? Anyone ever experienced this? If not, is there something else I should look at? I appreciate your help. Thanks. |
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Quoted:
I'm looking for some opinions on an issue I experienced yesterday at the range. I took out my new Colt LE6920 to sight it in and funcion test. I was shooting gen2 30rd PMAGS. Initially everything functioned fine but after about 20 rounds into my session the bolt stopped locking back on last round. I tested all three mags and they all experienced the same thing but it was intermitant. I then adjusted the stock to give me a better/tighter hold on the rifle and after that everything worked fine. Bolt locked back normal etc. So my question, would or can the grip/hold on the rifle have any affect on the ability of the bolt not locking backor cycliing correctly? Anyone ever experienced this? If not, is there something else I should look at? I appreciate your help. Thanks. It could I suppose, but you generally see that in handguns. When my 1911 was new it would jam whenever I let a girl shoot it, but I never had any problems. This seems to have remedied itself as parts wore in, but it was still a repeatable and duplicatable issue (if you want to call a weak grip an "issue") when it was new. You left out a key factor: What type of ammo were you using? Crap ammo like Tula won't reliably cycle one of my 6920's or my mid length 18" build. |
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Some possible issues and fixes.
1. Try some different ammo. It's unlikely Federal ammo could be the problem, and 7 to 8 years old is nothing. 2. Did you clean off the factory sticky preservative lube and re-lube? Colt's come with a rather sticky lube for shipping. You need to clean that off and re-lube with a using lube. CLP Breakfree is a favorite in the AR rifles and they tend to run better with plenty of lube. You also should clean the bore and chamber, and the buffer tube and spring. 3. Shoot more rounds. New rifles may need some break in to settle down. 4. P-Mags have a great reputation and it's unlikely you could get three bad ones, but try a different magazine like an aluminum. 5. It's not common, but possibly there was something about how you were holding the rifle. |
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I'd start here: Dirt, not enough/wrong lube, ammo or last: break in. Something is slowing the bolt from full travel. Could have a problem with the gas system, but a new gun that's not likely.
ETA: dFariswheel did a mutch better job. I did forget about the grease Colt uses from the factory. It's really sticky and will pick up dirt fast I'd imagine. Clean that sucker using a good degreaser then lube with an oil like CLP (or Mobile 1, my favorite). |
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Most problems relate to M.E.A.L.
M.E.A.L.: Magazines Extractor Ammunition Lube In your case maybe try different mags, ammo and check the lube, like what the other members said the factory preservative lube have to be completely removed, just adding lube to it will make it sticky and gummy. Your firing position should be slightly shoulder forward, with your firing shoulder lining up vertically to your firing foot's toe or even more slightly forward, and hold your carbine firm with full contact on your shoulder. I have two 6920 one I bought in 2011 and the other in 2012, degreased them totally and applied my favorite lube which is SLiP 2000 EWL (see lube instruction link below), my bolt assembly (only the bolt not the carrier) is very wet but not dripping, also the rails on the carrier are very wet. I used some very old ammo maybe around 20+ yr old Winchester white box XM193 Q3131, 10 yr old Canadian import surplus SS-109 62gr, new Lake City XM855, and Federal commercial bulk .223 55gr (from Walmart) all worked fine on my Magpul 20 and 30 rd PMAG, I fired from 200 to 300 rounds with each carbine for their fist function test and sight in. http://www.ar15.com/forums/t_3_7/548967_AR15_LUBE_POINTS.html |
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Quoted:
I appreciate everyone's responses! So at this point does anybody think I need to contact Colt or just try some of the things suggested? Is break in a potential cause on a brand new carbine? As a Colt fan, but not too happy with their CS, I would suggest trying the above responses. Did you clean and lube prior to shooting it? |
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Quoted:
I appreciate everyone's responses! So at this point does anybody think I need to contact Colt or just try some of the things suggested? Is break in a potential cause on a brand new carbine? I would suggest trying different ammo, if you could get some XM855 even commercial .223 like Federal bulk, then when shooting hold your carbine in a firm way, shoot it on a bench while pressing the buttstock to your shoulder and see if the problem is still there. AR don't really need any break-in just shoot it, with my former 6 and current 5 Colt ARs all of them I tested without FTF for 600 rounds or more before trusting them, all of mine worked fine without any problems. |
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So, I think I figured this out. I took the colt to the range Yest with another 100 rounds. For the first 60 or 70 rounds all pmags functioned correctly locking bolt back. Then I began shooting from bench rest type position and experienced the issue. I loaded two rounds in same mag again and it happened again, bolt didn't lock back. Then I fired the last 20 rds or so with no issues. Later I thought about all the responses I received and tried to deduce and eliminate one by one.
1. Under gassing should Also cause issues with ejecting and I had 0 ejection issues 2. Over gas should produce double feeds etc and experienced 0 of these issues The problem was so intermittent and odd I thought what could possibly cause such an intermitant problem? I thought back to my grip and problems I used to have shooting sig sauer pistols with "hight thumbs" and how the slide would not lock back due to my thumbs holding down the stop. I then examined my natural grip on the ar. I typically grip at the mag well ( I know this is not the proper thing to do ) none the less its comfortable and natural and never experienced issue before. I examined the location of my left thumb...right up against the bolt release. So then to test the theory further I gripped everything as normal pressure pushing the carbine into my shoulder and began to cycle the bolt aggressively making sure the bolt went all the way back. I then discovered that intermitantly the bolt catch would not engage on an empty magazine. I'm pretty confident that this was causing the issue especially coupled with recoil. Otherwise I experienced no issues with the colt whatsoever. It fired, fed and cycled everything! I will keep a close eye on this next range session but I think I got it. Thanks for everyone's input! |
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Quoted:
Yes, I cleaned and lubricated prior to shooting and llubrication was fairly liberal on BCG. If you used the wrong lube, that could well be the problem. Especially since the problem occurs after the gun gets hot. CLP, Motor Oil, Slip 2000 EWL (my favorite) are all designed to stand the heat. People on this forum will argue them all day long. But; the old timers will tell you don't use Rem Oil (or other light handgun oil) on an AR-15. It's like putting sewing machine oil in a Shelby mustang. There is a You Tube video that shows an AR-15 catching fire after many magazines of full speed firing. They do get hot. If it's dirty but lubed; it will still work. If it's clean but not lubed; it won't work. |