**UPDATE**Request help to diagnose a bad malfunction

**Serpico1985** · 09-20-20, 15:36

Roger that. We can do that lock back test. Seems like overgassing shouldn’t be the problem with the LMT Enhanced BCG since it bleeds off more gas than a standard BCG. Eventually my buddy will get a suppressor for it hence the LMT BCG.

I’m quite confident the ammo isn’t the problem. The gun should feed and cycle this ammo without issue.

**jbjh** · 09-26-20, 12:54

Any updates?

Sent from 80ms in the future

**Serpico1985** · 09-26-20, 16:48

Not yet. Can’t go to the range at will. Soon though hopefully

**MegademiC** · 09-26-20, 17:28

The only time Ive seen that malfunction, it was due to a bent extractor. Might want to try another bcg or bolt just to make sure there’s no issues there.

**1168** · 09-26-20, 18:27

I’ve seen similar with lightly gassed barrels and too much action spring.

Edit: look into Lysander’s advice first. He’s very knowledgeable. It also looks like there may be burring on the feed ramps. Push a cartridge in by hand with the upper off and bolt out. Push the tip up against the ramps. Does it snag?

**Serpico1985** · 09-26-20, 20:06

Thank you all for the thoughts. There is definitely a burr on the barrel ramp. You can feel it quite easily and catch a bullet nose on it. I suspect that the practice ammo was able to not get caught due to the smaller diameter nose which is why the rifle had zero issues for 300 plus rounds and many different mags. Then when he switched to the duty/HD ammo a problem surfaced in a couple different mags due to the larger diameter bullet nose.

Also, as far as gassing goes, the LMT enhanced carrier and enhanced bolt should prevent any over gassing due to the delayed unlocking and additional gas ports. Do you think the LMT part is enough to under-gas the rifle? Is the Super 42 spring known to be "stout" so to speak. I have A5's on all of my guns so I'm not current on the super 42 info.

We will test with a standard BCG soon.

But here's the question. If we determine that the problem is in fact the barrel extension ramp, how do we fix this? Seems like I could pull the barrel and very lightly sand and then cratex the ramp to eliminate the burr. I've seen School of the American Rifle on youtube do it albeit for a burr in a different location. I have a shop and quite a bit of experience with this type of work from building 1911's. But I know that AR's aren't my lane. Just curious what everyone's thoughts are if the burr is the problem.

Thanks again for your time and thoughts.

Zack

**Todd.K** · 09-26-20, 20:57

I'd put it that barrel in another upper to see if the feedramps match up better, if you can.

But if you know what cratex is you can probably smooth that out without bubba'in anything up.

**Todd.K** · 09-26-20, 21:02

And take the barrel out to work on it. If anything a slight step down from the upper is preferred.

**1168** · 09-27-20, 00:20

Originally Posted by Serpico1985

Thank you all for the thoughts. There is definitely a burr on the barrel ramp. You can feel it quite easily and catch a bullet nose on it. I suspect that the practice ammo was able to not get caught due to the smaller diameter nose which is why the rifle had zero issues for 300 plus rounds and many different mags. Then when he switched to the duty/HD ammo a problem surfaced in a couple different mags due to the larger diameter bullet nose.

Also, as far as gassing goes, the LMT enhanced carrier and enhanced bolt should prevent any over gassing due to the delayed unlocking and additional gas ports. Do you think the LMT part is enough to under-gas the rifle? Is the Super 42 spring known to be "stout" so to speak. I have A5's on all of my guns so I'm not current on the super 42 info.

We will test with a standard BCG soon.

But here's the question. If we determine that the problem is in fact the barrel extension ramp, how do we fix this? Seems like I could pull the barrel and very lightly sand and then cratex the ramp to eliminate the burr. I've seen School of the American Rifle on youtube do it albeit for a burr in a different location. I have a shop and quite a bit of experience with this type of work from building 1911's. But I know that AR's aren't my lane. Just curious what everyone's thoughts are if the burr is the problem.

Thanks again for your time and thoughts.

Zack

Take a picture, and mark the burrs on the photo for us, please. I’ve “fixed” a couple rifles that had burrs on the barrel extension with a tiny fine file (lightly) and some light polishing. Just want to make sure we are talking about the same thing.

**Serpico1985** · 09-29-20, 08:33

Prior to pulling the barrel I rechecked and there is a definite ledge where the barrel extension overhangs the upper M4 feed ramps. It is slight but it is there. I pulled the barrel and found that the left side ramp appears to have a chip missing out of it. Here are a couple of images to show it:

I have no idea how this happened. I think we would have noticed it when we did the original install. But I could be wrong. So it appears that it could be two things working together to cause feeding issues. A combination of a slightly mismatched barrel extension and upper AND a chipped barrel extension that exacerbates the situation. Thoughts?

I then put the barrel in the brand new stripped SOLGW upper and it seems to immediately be a much better fit. Here you can see that instead of overhanging there is a small gap between the bottom of the barrel extension ramp and the upper's M4 ramps. Couldn't get anything to catch on either feed ramp with this set up.

I took some 300 grit sandpaper wrapped around a wooden dowel and polished the barrel extension to soften the top edge of the chip, not wanting to leave the sharp top edge there. This is really about as mundane as can be. My buddy is OCD so I removed the parkerizing or whatever the black finish is on the barrel extension on the other side too so they would match.

I called my buddy and told him what I found. I think it would clearly be irresponsible for me to do anything else to the ramp at this point. The idea of taking a significant amount off the barrel extension to make it fit the ADM upper seems foolish. We came to the conclusion that he will get a dust cover and forward assist and we will complete this SOLGW upper and test fire. Hopefully next Friday.

Question is, does anyone think this ADM upper will work with other barrels? I'm not sure if they would replace it or agree that the ramps are a little shallow, which they seem to be based on the SOLGW upper comparison. Maybe if they won't replace it my buddy could get store credit or something.

Let me know what y'all think. I appreciate the comments and assistance.