New LMT Troubles

[AlohaChris]

Good Morning M4aphiles,

Having some troubles with my AR, looking for a diagnosis. First, some important details:

Gun: New, stock LMT CQB MRP with a 16" barrel.
Mods: Norgon ambi-catch, LMT ambi safety (I'm left handed)
Mags: Factory new Pmags, 30 rounds, windowed.
Ammo: .223 55 grain BVAC factory reloads, Brass.

So, I buy my first AR, sight it in at 50 yards without problems, fire about 100 rounds and sign up for a carbine course. The gun ran fine for about 200 rounds then I got a double feed malfunction like this:

http://img.photobucket.com/albums/v234/frontline_01/firearms/doublefeed.jpg

I cleared it, the instructor looked at it, said the bolt was a little dry and recommended I CLP it, which I did. The rest of the course (rounds 300-500), I had malfunctions. Some were double feeds as noted above, the others were (don't know what this is called) this: I locked the bolt back, insert a fresh mag (without slapping, not overloaded) and and hit the bolt catch/release. The bolt went forward, but jammed/stopped 1/4" from battery. When I tried to lock the bolt to the rear again, it was VERY difficult. The charging handle was stuck and it was very difficult to pull to the rear.

The cartridges that came out of the chamber had deep indentations just behind the "neck" area and some had the bullet knocked back into the case.

I got lots of "expert advice" including "AR's suck, get an AK", "Your need an enhanced bolt/heavy buffer" and "It's a new gun, it needs 1,000 rounds to break in".

What is going on here?

[Thomas M-4]

Was it 2 unfired rounds? The reason I ask is because sometime a failure to eject will be called a double feed.
A double feed is normally associated with bad mags but you say your using P-MAGS does this happen with one mag more than others?
Also Have you tried factory new ammo not reloads?

[AlohaChris]

I believe it was 2 unfired rounds, but perhaps not. The fist time it happened was in the middle of a string of fire, so it's possible it was an unextracted round. It was not mag-dependent. I numbered my Pmags (thanks to the great information on this forum), and it happened regardless of which mag was in the gun.

I sighted in with 100 rounds of Federal American Eagle Ammunition XM193C, 5.56mm, "Tactical" without problems. That said, I was sighting in, not running the gun hard while moving.

[rjacobs]

I locked the bolt back, insert a fresh mag (without slapping, not overloaded) and and hit the bolt catch/release. The bolt went forward, but jammed/stopped 1/4" from battery. When I tried to lock the bolt to the rear again, it was VERY difficult. The charging handle was stuck and it was very difficult to pull to the rear.

The cartridges that came out of the chamber had deep indentations just behind the "neck" area and some had the bullet knocked back into the case.


I have had that exact thing happen with a few of my re-loads that I believe I did not get sized properly, minus the bullet being setback into the case, have never had that. Have you tried running the gun with some factory ammo and not just the reloads?

[ralph]

Double check your mags..just because they're P-mags dosen't mean they can't fail..I've got 12 30rnd P-mags, and guess what? so far, I found 2 (NIW) and never used, with weak mag springs..they would'nt lock the bolt back when empty..I could probably call Magpul and complain,and probably get new springs sent to me, but why bother? I'll replace them with myself with high quality springs, I was told the springs Magpul uses in the mags are pretty much the same as USGI...

[Thomas M-4]

I sighted in with 100 rounds of Federal American Eagle Ammunition XM193C, 5.56mm, "Tactical" without problems. That said, I was sighting in, not running the gun hard while moving.

I would try more XM193 that is what I normally put through my LMT .
Then try some other factory new ammo wal-mart has federal bulk ammo that I try to buy its normally loaded warm:) Not weak like PMC and UMC :mad:.

[Robb Jensen]

Check your mag catch. The face of the button should be flush with the threaded part of the mag catch.

To adjust:
With an unloaded rifle, remove the upper from the lower.
Then use a pencil with an eraser on the end and depress the mag release but as far as you can. Then turn the mag catch clockwise, check to see if it's flush, repeat until it's flush.

Then try other known gun mags, run the gun wet and you should be good. Two live round double feeds are a mag problem or mag catch issue. A spent shell casing and a live round stoppage is typically a bad extractor, bad extractor spring etc. Sometimes the ejector can overpower the extractor. Be sure to lube up the ejector by dropping a drop of oil on the face of the bolt and work the ejector up and down a dozen times. On a CAR length gun like the LMT you might try running a Crane O-ring on the extractor spring if there isn't already one on it especially if you're running a CAR weight buffer (3.0oz).

[militarymoron]

this might be a stretch, but also check that the feed ramps on the barrel don't overhang the receiver. the ramps on the barrel should line up with the ramps on the receiver, or the bottom of the ramps on the barrel should be slightly forward of the top of the receiver ramps. i have one of the first MRPs that came off the line and had feeding issues. when i took a closer look, i discovered the slight overhang - just enough to catch a bullet tip occasionally. i corrected it, and the issue went away.

[AlohaChris]

Check your mag catch. The face of the button should be flush with the threaded part of the mag catch.

To adjust:
With an unloaded rifle, remove the upper from the lower.
Then use a pencil with an eraser on the end and depress the mag release but as far as you can. Then turn the mag catch clockwise, check to see if it's flush, repeat until it's flush.

Then try other known gun mags, run the gun wet and you should be good. Two live round double feeds are a mag problem or mag catch issue. A spent shell casing and a live round stoppage is typically a bad extractor, bad extractor spring etc. Sometimes the ejector can overpower the extractor. Be sure to lube up the ejector by dropping a drop of oil on the face of the bolt and work the ejector up and down a dozen times. On a CAR length gun like the LMT you might try running a Crane O-ring on the extractor spring if there isn't already one on it especially if you're running a CAR weight buffer (3.0oz).

I'll check it, but if it was a mag catch issue, wouldn't my mags fall out? All of my mag catch isin't 'flush' with the outside of the receiver because it's a Norgon ambi catch, the area towards the front is flush.

[AlohaChris]

I looked at the receiver, the feed ramps of the barrel appear to be very slightly recessed from the receiver, it does not appear to have overhang.

Another Clue?

While checking the receiver, it's dirty (obviously) from shooting, but there are all of these tiny, tiny (metal?) buttons, like sub-milimeter brass colored dimes in the chamber area. Hundreds of them. What are these? Are they normal?

[Robb Jensen]

I'll check it, but if it was a mag catch issue, wouldn't my mags fall out? All of my mag catch isin't 'flush' with the outside of the receiver because it's a Norgon ambi catch, the area towards the front is flush.

You're looking at the button on the shooters right side of the receiver. The threaded portion of the mag catch should be flush with the button.

[shootist~]

...the others were (don't know what this is called) this: I locked the bolt back, insert a fresh mag (without slapping, not overloaded) and and hit the bolt catch/release. The bolt went forward, but jammed/stopped 1/4" from battery. When I tried to lock the bolt to the rear again, it was VERY difficult. The charging handle was stuck and it was very difficult to pull to the rear.

This is caused by high primers - a primer that's not fully seated will cause the bolt to stop before it's fully in battery and you have to po-go to clear. You may not see it except when closing the bolt on a fresh mag.

[5pins]

We were providing range support for some ROTC’s that were qualifying with the M16. We had a lot of double feeds and live rounds getting trapped between the bolts and charging handles. I have no idea where they acquired the rifles but they were in bad shape. Turns out that the mag catch springs were weak and replacing the springs took care of the problems. Until we ran out of springs, then we would just turn the catch in one rotation.

[AlohaChris]

You're looking at the button on the shooters right side of the receiver. The threaded portion of the mag catch should be flush with the button.

OK, I looked at the mag catch button and the threaded portion wasn't flush with the button. I turned it two full rotations clockwise, but then it was protruding a bit (felt like the mag catch button had a stud in the center) so I backed it out one rotation and it's perfectly flush with the surface of the button. This is the only thing I changed (adding the Norgon ambi-catch) after sighting in the rifle. If it was causing the problem, wouldn't it manifest itself earlier in the day?

I don't understand why this will make an impact.

[fdxpilot]

Have you tried some good (I.E. known quantity like Federal or Lake City) ammo to see if it feeds OK.

[HES]

The gun ran fine for about 200 rounds then I got a double feed malfunction like this:

http://img.photobucket.com/albums/v234/frontline_01/firearms/doublefeed.jpg

Hey nice pic there. Looks familiar :cool:

Seriously though this isn't an LMT issue. I created that pic the other year when my wife was having a problem with her 6920 during an Appleseed shoot using Federal XM193.

We havent been able to recreate that problem since.

[Oniak]

At a recent carbine course, the instructor told me how he had recently bought a case of .223 that ended up giving him nothing but problems. I asked what ammo it was and he told me BVAC. I would try some other ammo and see if you are still having problems.

[AlohaChris]

Hey nice pic there. Looks familiar :cool:

Seriously though this isn't an LMT issue. I created that pic the other year when my wife was having a problem with her 6920 during an Appleseed shoot using Federal XM193.

We havent been able to recreate that problem since.

Yes, the search function is my friend. I read your thread, but didn't see what, if anything, you did to "cure" it.

I didn't shoot any of the BVAC ammo prior to the course, just the Federal. Thinking back, early in the day we were mostly doing single shots and slow fire. The troubles began when we started "running & gunning". I'll have to get some more Federal and see if that doesn't fix it.

Am I correct that .223 and 5.56 are the same dimensions, but 5.56 is loaded to higher pressures?

[HES]

Check out this thread (https://www.m4carbine.net/showthread.php?t=53093) for your answer

[AnimalMother556]

You're looking at the button on the shooters right side of the receiver. The threaded portion of the mag catch should be flush with the button.

I'm having trouble wrapping my mind around this, how exactly does this cause double-feeds? On my rifle the threaded post is just below flush, if I turn it one more turn the post sticks out higher than the button. Which way should I leave it? Colt mag catch and button BTW.

[Irish]

I could probably call Magpul and complain,and probably get new springs sent to me, but why bother? I'll replace them with myself with high quality springs, I was told the springs Magpul uses in the mags are pretty much the same as USGI...

Told by who?

[ralph]

Told by who?

Grant at G&R...who also told me he replaced his with chrome-silcon springs..

[Robb Jensen]

I'm having trouble wrapping my mind around this, how exactly does this cause double-feeds? On my rifle the threaded post is just below flush, if I turn it one more turn the post sticks out higher than the button. Which way should I leave it? Colt mag catch and button BTW.

A too lose of a mag catch can allow the mag to move around too much. Can cause double feeds and all kinds of weird stoppages.