What is wrong with my AR-15???

[Spiff]

Check your rings, damnit. Take out the BCG, remove the bolt from it, and see if the ring's slots are lined up. They should be staggered.

This does not make a bit of difference on a properly functioning AR.

Make sure the gas key is tight, make sure the roll pin is holding the gas tube into the FSB properly, make sure you've got oil in all the right places, make sure you've got good mags, and make sure you've got good ammo.

 

[ArGyLe64]

Do you know if you have the correct buffer weight and spring?

It's whatever buffer and spring that came with the rifle straight from the factory.

 

[ArGyLe64]

This does not make a bit of difference on a properly functioning AR.

Make sure the gas key is tight, make sure the roll pin is holding the gas tube into the FSB properly, make sure you've got oil in all the right places, make sure you've got good mags, and make sure you've got good ammo.

The gas key is staked. The roll pin holding the gas tube was a pain in the arse to get into the FSB but after 2 hours I got it in there. I use PMAGS and I've been shooting Winchester, PMC, and Hornady. I guess tomorrow I may be able to try a heavier buffer out at H&H and see if that fixes it. I'll give it a good cleaning tonight.

 

[Spiff]

You're going to properly lube it too, right?

 

[ArGyLe64]

CLP all the way.

 

[SMS]

Ditto on the rings not mattering....I've seen 'em run with a single ring.

First suspects, and quickest to eliminate: Ammo and Mags....have you tried multiple?

Otherwise I'd suspect the buffer/spring, but since its a new LMT I'd be surprised.

 

[blackknight22]

I would check the gas key, I see you advised it was staked, but is it sitting correctly on the carrier ?
Is the ammo your using 223 or 5.56 ? If all 3 gas rings are on the bolt I doubt them being staggered would be the problem, but would look to see if they have the approximate same size gap.

So my guess so far,

check bolt carrier key
check ring gap
does the bolt and carrier run smoothly back and forth in the upper
try ammo that is marked 5.56
try different mags
check buffer & spring to see that they are correct for your gun

 

[ArGyLe64]

The Winchester 5.56 ran flawlessly through the gun but the other .223 brands are when problems occurred. The gas key appears to be okay.

 

[doctorjj]

Was it sloppy wet with lube? Don't skimp on any AR but especially on a new one.

 

[peanut]

Weak ammo? What buffer and carrier does it have?
Try this: cock the hammer, remove buffer and spring, close and pin upper to lower, pull charging handle back, is it abnormally hard to pull the bolt back? It should be relatively easy. It should rechamber by bouncing the muzzle into the carpet with one or two bounces! Reinstall spring and buffer.