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Posted: 10/8/2004 5:18:21 PM EDT
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Hello, Well, in the process of sighting in the AP and new Larue BUIS on this new upper, I ran into a small problem. I was at a range that requires me to load 1 round at a time. I know, I know, dont hassle me about that range, but it's the closet place that has a 50 yard marker for me to sight in my stuff. At the time, I had my empty BM 10rd magazine in the rifle and was loading each round manually through the ejection port, into the chamber. At first, I wasnt having any problems. But after about 30 rounds or so, the bolt wouldnt lock up after the rifle was fired. This happened a few times, so I figure could be a possible magazine problem, so I switched to my trusty DPMS 30rd magazine. But the problem persist. So when this happened, I had to pull the charging handle back. But doing so, each time, it locked no problem. A couple of times, when the bolt was back, and I hit the bolt release, the bolt wouldnt go forward. It seems like it was stuck. I had to slap the side of my rifle before it would go forward. So I put about 75 rounds through her, and switched to my BM to resight her in. I had no problems with either BM or DPMS magazines. So, anybody may know whats up? PS, in the LMT upper, I'm using the LMT enhanced bolt and standard carrier |
Theres nothing wrong with LMT. Every manufacturer goes thorugh growing pains, but by and large LMT's products are excellent and better than most. |
+1, I have had zero problems with any of my LMT uppers on numerous lowers. I also use only Colt BCGs |
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It is certainly possible we sold the upper, we sell a lot of them. LMT build their uppers though, we don't. Hard to diagnose without some hands on, but I have seen this with some ammo that has dirtier than normal fouling. If it loaded fine for 30 rds, then the carrier started hanging up it could be mechanical, as others have suggested, or it could be from accumulated fouling in the receiver and on the carrier. We break in a lot of AR's, all our precision builds are fully function and accuracy checked prior to shipping, including barrel break in. That adds up to a lot of rounds down range with new uppers and BCGs. Bottom line, break-in goes best with everything wet. Normal lubrication doesn't cut it during the first few hundred rounds in many cases. If something is not obviously loose, I would hose the carrier and receiver inside with LCP or a good synthetic oil (Amsoil 20 wt works great for break-in, but not good to leave it in the gun, lube, shoot, clean when done). If the carrier starts behaving as soon as it is well lubed, ggod to go. If not, time to look further. |
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Does the boltstop/release work when the weapon is cycled by hand? Have the magazines your using been "proven" in a solidly functioning weapon?
Indeed. Apparently when LMT's are w/o flaw they are an excellent example of the AR family of weapons, w/ excellent features and reliability records. However they seem to be having some trouble w/ QC as they grow and meet a growing demand for their products. Wonder why ther's a growing demand...? That's normal in varying degrees from any compny, no less so from a weapons manufacturer. What's important is that they acknowledge their mistakes and as a testament to their quality replace/repair whatever mistakes they've allowed to get through. /S2 |
The reason you don't drop a round in the tube and release the slide on a Sig, 1911, Glock, etc. is you could break the extractor or wear out the extractor spring. Also, if the weapon you are shooting is extremely dirty, releasing the slide on an already chambered round may cause a misfire. Some heavy lubricating oils cause the same problem. - The dirty/clogged firing pin rides the bolt forward and strikes the primer with enough force to set it off. The bolt assembly slows down when it strips a round from a mag. Also, there isn't a direct strike from the bolt face to the primer when chambering from a mag. I wouldn't drop one in the tube, best to use a mag. 
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Thx for taking the time to look at my post. Yes, I did receive the upper from MSTN. The lower is a Mega, with Bushmaster parts in it. Just to make it clear, the problem with the bolt not locking back, did not happen everytime. It happened either every other round, or 2 out of 5. I can NOT repeat the problem at home. Each time I manually pull the charging handle with an empty magazine, the bolt/carrier will lock back. Each time I hit the bolt release, it slammed forward. I shoot Q3131A exclusively. I'm using a Magpul M93a stock with a LMT H-Buffer and spring. The 2 magazines I used, BM 10rd and the DPMS 30rd magazines, are proven magazines which work flawlessly, in my Bushmaster rifle. As stated in the 1st post, I switched rifles, to my Bushmaster and used these 2 magazines. Functioned perfectly as always. Since I couldnt repeat the problem, I tore the upper down and cleaned it up. The gas key is on tight. As I was inspecting the parts I saw 2 things that raised a concern. 1) It appears, on the backside of my carrier, part of the edge of it isnt smooth. Cuz it's cutting into my buffer's face. I have since smoothed out the imperfection, and hopefully, wont be a problem. 2) I noticed a "cut" in my cam pin. At least I think that's what it's called. It looks like something has slammed into it, making a small indentation. I looked at the bolt , but I dont see any markings on it that could have caused this. But the shape of the "cut", fits the bolt though. Here is a pic of what i'm talking about. Now, I know that wasnt there when I first got the upper. I took apart the upper and cleaned it before I shot it for the 1st time.   When I shot the LMT upper, in my opinion, it was pretty lubed up. It wasnt dripping or anything like that though, but it wasnt bone dry. I wont be able to shoot the upper til later this week. So we'll see what happens then. If the bolt still wont lock up, I'll try switching the LMT upper onto my BM lower and see what happens. |
I actually received the bolt/carrier through a different dealer. In the pic, it not very clear. All that white isnt the indention. It's just missing the finish, and at the bottom of it, is where there's a "cut" in it. |
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check out this thread: Problems with LMT It appears many people have been experiencing problems with the cycling of their weapon with LMT's enhanced carrier. You might want to swap out your LMT Bolt group with the bolt group from your bushmaster and see if you have the same problem; if you don't, you'll know it was the LMT bolt group that was causing the trouble. People have also complained of other problems with their LMT products in these threads: excessive windage Problems with LMT/CRANE STOCK Poor quality control of LMT buffer tubes LMT in other words is going down hill. |
Is this appropriate? I was under the impression nothing should be "cutting" or battering the buffer's face. |
PS, what is LMT's website? I cant see to be able to find it. |
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Had a shooting feast with a couple of friends today. For one of them, it will be their first time ever shooting a handgun and rifle. For the other, he has his dad's glock, but never fired a rifle before. Lets give names to them, so it's easier to write.  Beki was scared to shoot my handgun, rifle, and my friend's glock. She wouldnt shoot anything for the first 30 mins. Eventually, we manage to get her to shoot my HK USP 9. Well, on the last round, she lifted her off hand thumb, and got smacked by the slide. Hit the end of my nail. Caused a little bleeding, but she toughed it out.  Anyways, my other friend, Mike shot my BM, and loved it. Soon, we convinced Beki to try the rifles, and she couldnt get enough of it. Now to my problem. Well, my LMT+Mega lower is an unreliable AR. Everytime I loaded a magazine, and try to load a round into the chamber, it would NOT go forward. It would hang. I can see the round halfway out of the magazine though. If I pull the charging handle again to load it, that round will then go into the chamber. This happened everything time I think, if not, 95% of the time. A few times, when firing, it will malfunction. Bolt wont go all the way forward, in a middle of a magazine. Happened 3 times on a single magazine. Had to slap the forward assist. It is NOT the magazines, at least i dont believe it is. I used the exact same magazine for my BM rifle, and they performed beautifully. I wouldnt let my friends shoot the LMT combo because if something goes wrong, they wouldnt know.  I figure, since I built the Mega lower myself, maybe something is wrong with that. So I put that to the test. I swapped my BM upper and mated it down to my Mega lower. LMT upper now on BM lower. BM upper+ Mega lower= no problems. LMT Upper+ BM lower= same problems. It was getting late. Next time, I will swap bolt/carrier and see what happens. |
Umm, one would like to think that LMT would install the proper extension, since their receivers have the machining for the feedramps  The first one I had, had similar problems. I RGA'd it for another upper, and that one runs. |
Is LMT upper a tru put together by LMT or did you buy the parts and put it together? If you put it together you probably have the wrong barrel extension. LTM uppers require a M4 barrel extension. the wrong barrel extension can have the bullet tip hang up on the overhang. |
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I've got an LMT 16" upper that I bought from MSTN. I don't think I've got "one of the few that actually works" LMT uppers, I think I've got an "average" LMT upper. I've fired over 1000 rounds through it with exactly one failure. That failure was caused by a first time AR shooter. She had the ejection port right up against a barricade, so the spent brass had nowhere to go. Can't hardly blame the upper for that. I'm using my '93 vintage Colt Lower, carrier and bolt (which have seen probably 8,000 rounds.) I've got zero problems. The fit and finish is fantastic, and everything is "true." Can't complain. I bought the upper a few months ago. |
I'm told it was LMT who built the upper. It has the M4 cut out in the receiver. The only thing i built was, the Mega lower. And as of right now, I can scratch that off the list of cause. I need to find some dummy rounds so I can cycle some rounds safely. Where can a person find dummy rounds? |
Anyways, I think I may have found out the problem, but i need a different lower, with a different stock to prove it. What I believe is happening is, the bolt and carrier isnt going all the way back when fired. It's stopping about 1/2 an inch short. So when I shoot the last round of the magazine, the bolt will lock back, but it's actually locked onto the carrier, not the bolt. With this, the bolt is directly behind the round on the next magazine. When hitting the bolt lock release, since the bolt isnt fully back, there isnt enough force to push out the following round. Now, how do I fix this, or what causes it? Remember, I'm using a Magpul M93a stock, with a LMT H-Buffer and carbine spring. This combination runs perfectly on my Bushmaster upper, why not the LMT Upper? I can manually lock the carrier back, by using the holding down the bolt catch on the LMT upper. If I pull a little bit harder on the charging handle, it will then catch the bolt and lock it in. I can NOT catch the carrier with my BM upper. I have to pull the charging handle all the way back, in order to lock the bolt. |
That could, possibly, create a dangerous headspace condition. You should be able to swap carriers though. |
Yea, i'm pretty sure. The buffer is a H-Buffer, which is much shorter than my old A2 buffer. The spring is shorter, than my old A2 spring. |
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