AR Sponsor
Posted: 4/19/2008 8:54:09 PM EDT
|
I've got an LMT M4 upper half with 30 rounds through it. It is exibhioting afew problems. When feeding (by hand) the bolt is fairly slugish and often does not fully chamber the round. (Yes I am pulling the charging handle fully to the rear and releasing it.) The problem persists with several different mags USGI and P mags. Often when pulling the charging handle to the rear it sticks and takes quite a bit of force to pull it back, this has lessened since it was brand new, but is still noticeable. When firing I had to slam the but of the rifle on the ground to get it to extract more than once. Inserting a round into the chamber by hand with the BCG removed the round tends to stick in the chamber with and not fully seat about half the time. Again this is with several different types of ammo. All problems seem to persist wether the upper is on a lower or not. Ejected rounds all have pretty deap scratches in the projectile and ejected brass has scratches running from the neck to the head. So I'm thinking there is a bur in the chamber though I can not make it out visually. Any other thoughts? Also there is some premature wear inside the reciever and on the cam pin. the wear may indeed be normal, most of the M16s I dealt with in the service were quite old, however my other ARs never showed this much wear this quickly. I could really care less about the cosmetic issues however I would tyhink it should hold up better than this. All in all this upper has been a dissapoint ment to date. I've owned several other Ars over the years, RRAs, Bushys and other LMTs and never had one that would not feed reliably before. I'll be calling LMT Monday to see what they can do inless anyone here has an ideas that may fix the problem. The round on the left shows the typical scratches on the projectile.  The bottom round shows the typical scratches in the brass.  Here's the best pic I could get of the chamber and feed ramps, not very helpfull I know.  Here are a couple shots of the finish wear I was talking about.  
|
|
Those scratches on the rounds are completely normal. LMT's come with a dry lube inside the upper reciever. ITs sorta a grayish color. It will wear off pretty quick and is again completely normal. Has the upper and BCG been cleaned properly? A lot of issues people have with new rifles are a result of not cleaning the thing before shooting it. Clean, and lube well. Inspect the BCG for any burrs. Make sure the ejector works properly, and check the extractor to make sure the lip is cut properly. Different rifles will wear differently due to small variations during manufacturing even though the parts are within spec. Nothing to worry about there. Check the bolt lugs and make sure they are cut cleanly. Your chamber might be cut slightly small and that is why the rounds are getting caught up. What type of ammo are you shooting? You said you bought it with 30 rounds so that means it was used correct? The person you bought it from might have shot laquered Wolf, and shot more than 30 rounds through it. That will cause a "sticky" chamber so make sure you clean that well. |
|
No I bought the upper brand spanking new, I have fired about 30 rounds through it. Everything on the BCG seems fine and yes it was properly cleaned and lubed before it was ever fired and has been cleaned and lubed since. The gray in the reciever may indead be a dry lube however it does not come off with any ammount of scrubing and was not noticeable the first time I cleaned the rifle. Live fire ammo was WWB and Adcom, Ive tried hand cycling it with my reloads, Adcom, LC and WWB all with the same results about half the time the round does not completely fall into the chamber freely. |
Adcom isnt quality ammo. That dry lube comes off pretty easy, and the steel BCG will take it off quickly. Nothing to worry about, and its not supposed to be long lasting. Do you have another lower to try the upper on? How about a different bolt or BCG? Charging handle? Thats one reason I like keeping spare parts around so when an issue like this does come up I can swap parts until the problem is isolated. I would swap any parts that wear against another in regards to the BCG moving back and forth from easiest to hardest until the issue is located. I recently had an issue with a BCG sticking on a new upper. Turns out the charging handle was slightly oversized and was rubbing the little flat section it comes into contact with on the lower. Replaced with new unit and its smooth as glass now. |
Well took it out again today and brought along some spare parts, Turns out it was the cam pin. Popped a new cam pin in and it worked just fine. The old one appears to be soft. Where it makes ocntact with the carrier toward the bottim of the cam pin the metal has formed a pretty good bur. I've included a picture but doubt you can tell from it. The only way I could tell was by running my finger across it. It fells like the bur is about 3/32" and it noticeably makes the bolt drag in the carrier. I ran about 200 rounds through it after the swap with no problems.
|
AR Sponsor