LMT AR-15 shoots only one at a time...

[bosaw]

I have a Lewis Machine and Tool AR-15 and I can't figure out why it won't chamber another round. I charge it, fire, and click. I pull the charging handle back and no round was chambered. The one I fired was ejected, but it's like the bolt didn't go back far enough to pick up the new round.

I checked the magazine and used several different ones in several different AR's. It is definitely not a magazine issue, it is a gun issue.

I was thinking maybe the gas tube wasn't connected good enough to blast the carrier back far enough, but it appears to be all good and sealed well.

Let me know if you have experienced this before and what the issue was. It's driving me crazy.

Thanks,
Bosaw

 

[Mgderf]

You are under gassed, or over tensioned on your buffer spring, or both.

You can be under-gassed if your gas block is not at true top dead center. It can be a fraction off center, or not far enough back on the barrel to index with the gas port in your barrel.

It could also be a VERY dirty gas system. Maybe a small chunk of carbon build-up blocking the gas port.

Could be a lot of things, but it sounds like you're under-gassed.

BTW- 2

 

[Double T]

Factory loads? Handloads? How wet is your carrier? Can you press the buffer into the tube easily (spring)? Is the round being stripped at all or is it just chilling in the magazine?

Pretty hard to diagnose without knowing a bunch of stuff

 

[mvician]

Which LMT do you have?
What ammo are you using?
Is your bolt and carrier lubed?

 

[bosaw]

Based on what I've experienced, I'm gonna guess I'm under-gassed. I'm thinking about blasting out the gas tube with some compressed air and seeing what that yields.

Buffer spring feels smooth. When I pull the bolt back, I feel the carrier going over the hammer as being the only significant resistance.

I've only shot .223 loads (PMC brass, WPA steel, and Lake City reloads that I reloaded with 55 grain HP's and 25 grains of powder). I haven't put anything through it rated at the 5.56 NATO power.

The rounds were just chilling in the mag. I just bought the gun a month ago and haven't got to shoot it too much. When I did today, I was scratching my head.

I'll start with the gas tube and see what happens.

Thanks for the tips. I'll try to get back on here tomorrow and give a follow up.

Best Regards,
Bosaw

 

[bosaw]

Which LMT do you have?
What ammo are you using?
Is your bolt and carrier lubed?

Ammo I answered, but as far as lube,... Not with grease like lubing a car, but it's well taken care of and is loose just like all my other AR's.

Best Regards,
Bosaw

 

[bosaw]

It's a Defender 2000

 

[cwillour]

I've only shot .223 loads (PMC brass, WPA steel, and Lake City reloads that I reloaded with 55 grain HP's and 25 grains of powder). I haven't put anything through it rated at the 5.56 NATO power.

Not certain about your reloads as it depends on the powder, but the PMC and WPA loads have a reputation for being a little light.

If you are reloading yourself, you might try a few loads edging towards max for your powder (if you are not already there) and see if it makes a difference.

Also, you might want to get the bolt sloppy wet for the first couple hundred rounds. I have seen a few that just would not run with a normal coating until they had a little wear.

Another easy thing to check is whether your gas key is tight.

 

[bosaw]

Not certain about your reloads as it depends on the powder,...

If I can remember correctly, the book showed .223 being 24-25grains of powder and NATO rounds being ~32grains for the projectile I was using. For plinking and sighting in and testing, I prefer to load the lighter rounds to make the brass last longer.

But the whole point is, side by side, next to my two Bushmaster XM-15's, my Remington R-15, S&W M&P AR-15, and the Rock River LAR-15 I just built, the LMT does not repeat.

I have troubleshot it enough to know it's a gun issue and not a mag or ammo issue. All functions on the LMT are just as good as any other AR's I have so when someone said under-gassed, that sounds right. I'm going to try that out and see what happens.

Thanks for all the input so far.

Best Regards,
Bosaw

 

[cwillour]

Have you tried swapping the bolt from one of your other ARs into the LMT?

You might even try swapping both the BCG and lower from one of your other builds. It could still be that the upper has an issue with the lighter loads you are using (whether due to being under-gassed or not), but at least you can rule a few more things out.

 

[bosaw]

Have you tried swapping the bolt from one of your other ARs into the LMT?

Nope, but that's another good idea. If it is a bolt issue, I'm glad I have another one ordered...

Man, I like the noodles here!

Thanks again,
Bosaw

 

[black label]

Do you have an adjustable gas regulator? I have an lwrc repr ( I know not the same gun). But it has a 4 position gas regulator, one of the positions is for a single shot, so you can run the gun like a bolt action.

 

[cwillour]

You might also want to look behind the gas block to see if there is excessive residue, which could indicate an alignment issue causing the system to be under-gassed. Generally speaking, a little residue is to be expected, but if you have a large streak there is a good chance your gas block is not sitting correctly on the barrel port.

 

[thoroughbred]

Take some gun scrubber with the thin red tube nozzle and spray it directly in the gas tube and look to make sure there are no leaks in the block and that it runs out the barrel...other than that just because the charging the rifle is smooth doesn't mean your ammo has enough power to cycle it...my lmt mrp is smooth as silk even when it was brand new...try some mil ball ammo and see if that cycles it if it does the rifle probably just needs to be broken in a bit

 

[bosaw]

Do you have an adjustable gas regulator? I have an lwrc repr ( I know not the same gun). But it has a 4 position gas regulator, one of the positions is for a single shot, so you can run the gun like a bolt action.

No gas regulator that I know of. it just seems it's not getting a good blow back. I'll check and advise.

Best Regards,
Bosaw

 

[djhuckle]

No gas regulator that I know of. it just seems it's not getting a good blow back. I'll check and advise.

Best Regards,
Bosaw

Regulators are usually on piston rifles (probably only 1% of ARs). (exception: Colt Competition Rifle "Pro" Model CRP-16).

 

[bosaw]

Regulators are usually on piston rifles (probably only 1% of ARs). (exception: Colt Competition Rifle "Pro" Model CRP-16).

No piston rifle here...

 

[mvician]

Guessing this is a new Defender?
Your other AR's have a bigger gasport is probably why that ammo will cycle in them.
LMT is amoung the few that use the correct size.

Has anything been changed from "stock"?

Where are you located?

 

[Hookeye]

Load
Manually
Tiger

 

[rvb]

I've only shot .223 loads (PMC brass, WPA steel, and Lake City reloads that I reloaded with 55 grain HP's and 25 grains of powder). I haven't put anything through it rated at the 5.56 NATO power.

The rounds were just chilling in the mag. I just bought the gun a month ago and haven't got to shoot it too much. When I did today, I was scratching my head.

So it worked, then it didn't?? How many rounds before the failures started? Same ammo?

Have you tried the basic under-gas test of firing one round w/ an empty mag and seeing if the bolt locks back?

If it worked before it didn't, it could be a gas issue, but only if something failed. Check alignment of the gas block to make sure it didn't get knocked around and any screws are tight (vertical and ~1/32" between it and the shoulder on the barrel... the hole in the blocks are pretty large and pretty forgiving of 'perfect' alignment). Check the pin is in place for the gas tube, check the carrier key is mounted solidly, and check the gas rings are ok (pull the bolt fwd in the carrier, place it on the bolt face pointed up on a table, if the carrier slides down the rings aren't sealing enough).

If it's still basically new (<200 rounds), clean it, lube the snot out of the carrier, and see if it breaks in a bit. People poo-poo a break-in period, but I've seen dozens of rifles that didn't run 100% until they got a couple hundred rounds in (primarily the carrier raceways smoothing out).

Did you're shooting style change between trips to the range (eg standing, w/ a firm grip the first trip, then held loose on a bench the second trip)?

Do you know what buffer it's using?

As mentioned PMC/Wolf is known to be weak stuff. Pick up some M193 and see what happens. If nothing else, put a couple hundred rounds of M193 through it to get broke in, then come back to the PMC/Wolf plus your handloads and see what happens.

-rvb