AR Problems

azn_hitman

azn_hitman

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hello all,

i recently built an 10.5 inch shortie AR from parts. took it to the range for the first time yesterday and kept getting malfunctions in the form of a few things:

-on the last round, the bolt fails to stay to the rear
-the round is wedged between the chamber and the mag at an angle, with the bolt resting on the side of the round. the casing is usually dented by the bolt
-the bolt fails to pick up rounds when cycling either being cocked or while shooting

the specs of the AR:

-LMT 10.5 inch upper
-LMT full auto bolt
-STAG stripped lower with DPMS parts kit
-Mil spec buffer tube with H marked buffer.
-PMAGS were used

i tried cleaning the rifle, but the problems still exist. now i am feeling pretty hooptied and out of ideas. any ideas? thanks in advance
 
Your rifle is short stroking, the bolt is not getting enough gas to open all the way. 1. Make sure your gas block is directly over the gas hole. 2. A little lube doesn't hurt. 3. If the gas holes are lined up, try getting a lighter buffer. This is a common problem with the AR short barreled guns, most of your powder will be on the snow in front of you, not all of it gets burned therefore you get less preasure.

Scott
 
What are you using for ammo?

And check the mags for function with another upper (known to work reliably) ... although I suspect this isn't this problem its worth checking.

Lube is a good idea. I have found wheel bearing grease to work well in AR15 rifles. Clean first.

Other than that you are looking at gas tube issues (see previous post by m39a2). Is your gas block original to the barrel or some aftermarket clamp on/ screw on type? These can be problematic. I have found the original FSB setup solid and quite superior.
 
thanks for the replies. the ammo i used was the winchester .223 55 gr white box. the gas block is the original one on the upper in the form of an A2 sight post. where would be a good source for hi temp wheel bearing grease? all i could find are the industrial tubs.

thanks,
 
Canadian Tire should have some high temperature wheel bearing grease in stock in tubes.

Did you install the gas tube yourself? As mentioned before, check that it has been properly installed and has not wandered.

It sure sounds like a gas problem, but trying the simple stuff first won't hurt. The ammo you are using should have enough power to work the action, from my experience with it.

I have had feeding/cycling issues in my rifle but they were associated with a bad magazine and an aftermarket gasblock which was worn out and leaking gas. I have also found one brand of ammo would not work the rifle, although I'd like to test further before I mention the name (not Winchester). At this point I doubt that grease will be the answer (it should help a bit, so who knows?) and would be very interested in the history/assembly of the upper. Beyond that there is checking the measurements of the gas port on the barrel, but that is an area beyond my experience and knowledge.
 
what kind of ammo are you shooting - the LMT is designed to shoot M855.

Although almost all work with run of the mill .223, the factory only states that they work with M855.

IIRC, the LMT does run on the H buffer and mine would run on 2H. One thing you could check - make sure you are not using a rifle buffer spring.

The first thing I will do - inspect the bolt carrier and bolt. Switch the bolt group - if not switch lower -

I once have a "rebuilt" Colt M4 upper that would refuse to work on one lower, and work magically on the other. THis can be some weird tolerance stacking going on.

Failing that- it is the gas port. The last thing you want to toy with. That should be a factory warranty work.

Another possibility - is it a real LMT factory or someone claimed it to be LMT. All new LMT has laser engraved LMT logo on the side. The old ones don't but you can tell it is LMT the other way.
 
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azn_hitman said:
(...)the ammo i used was the winchester .223 55 gr white box. the gas block is the original one on the upper in the form of an A2 sight post(...)
Click to expand...

Wasn't there a thread talking about how LMT's gas ports are a bit smaller than some of the others because they build the rifles exclusively with LE/MIL in mind, and thus expect you to run full pressure 5.56?

Or maybe I saw that thread on arfcom... cant remember now.
 
i recently built an 10.5 inch shortie AR from parts.
Click to expand...

So, your upper is not factory original. Did you use a new gas tube? Is the front sight tower factory original? Does it look like someone messed with the front sight pins?

the bolt fails to pick up rounds when cycling either being cocked or while shooting
Click to expand...

If the Carrier is not picking up a round when you cycle the action by pulling the charging handle all the way back and letting it go so it strips a new round under its own force..... I bet that you're using a rifle buffer spring instead of a carbine spring like GT mentioned earlier.

-STAG stripped lower with DPMS parts kit
Click to expand...

If I were you, I'd lose ALL the DPMS parts installed in your lower. A Stag parts kit is a good idea. They're readily available from Arms East.

-PMAGS were used
Click to expand...

Not saying there's anything wrong with PMags, but have you tried conventional mil-spec mags.

Make sure your magazine is latched in assertively and held by the magazine catch properly.

Believe me, there's nothing wrong with the gas port size in the barrel. I would not #### with it. I would make sure there aren't any obstructions in any part of the gas channel. Remove your gas tube, using an air compressor if you have one, blow the hole in the front site tower clean of obstuctions if any.

Count the coils on the spring you have installed. A carbine spring has 36 coils and a rifle spring has 44.

Check the carrier key. Make sure it's tight and free from obstruction.

Are your gas rings intact. If you hold the carrier vertically with the bolt at the bottom, does the bolt fall out. If so, you need gas rings, or new ones.

And definately, get yourself some real ammo to run with. A shorty AR is not a varmint rifle.

Aside from that, send me the gun, I'll fix it for you. Where abouts are you BTW?

Regards.
 
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so i detail stripped the AR today to clean it and to check a few things that was mentioned. so i figured i would clarify a few things.

-the upper is, in fact, all LMT factory. the only changes i did was a KAC RAS II. it is listed as a US NAVY CQBR upper, with the LMT laser engraving.
-the buffer spring is a carbine spring. 36 coils.
-i mixed up the bolt carrier group. the BCG that was in the shortie was from my 16 inch Bushmaster XM15E2S so i swapped the LMT BCG to the shortie. this may solve the problem.
-got some RUAG 5.56 to test the rifle with.
-got a 5 round stubby mag that came with the bushmaster to use at the range.

going to test the rifle again this weekend. we'll see what happens
 
In My LMT ,

I shoot cheap UMC 55gr, NO FTF, NO FTE, NO FAILURE of any kind.

May be your problem is your lower,
 
azn_hitman said:
so i detail stripped the AR today to clean it and to check a few things that was mentioned. so i figured i would clarify a few things.

-the upper is, in fact, all LMT factory. the only changes i did was a KAC RAS II. it is listed as a US NAVY CQBR upper, with the LMT laser engraving.
-the buffer spring is a carbine spring. 36 coils.
-i mixed up the bolt carrier group. the BCG that was in the shortie was from my 16 inch Bushmaster XM15E2S so i swapped the LMT BCG to the shortie. this may solve the problem.
-got some RUAG 5.56 to test the rifle with.
-got a 5 round stubby mag that came with the bushmaster to use at the range.

going to test the rifle again this weekend. we'll see what happens
Click to expand...

So... were able to test your gun this weekend?

Just a stupid thought.... wondering, there wouldn't be a buttcap spacer from an A2 stock in your buffer tube, would there?

What's puzzling me is you mentioned that you cannot pick up a round even cycling the action by hand. That limits the possibilities right there.

As a similar example of silly things that happen, say you install a long, A2 buttplate screw onto an A1 buttstock that really needs a short screw, the long screw will impede the full travel of the buffer. The buffer pad would hit the tip of the protruding screw and the gun would short stroke.

Regards.
 
-the bolt fails to pick up rounds when cycling either being cocked or while shooting
Click to expand...
I missed this part in the first reading.
Not to be an ass, but did you double check the mags were fully seated?
Can you manually engage the bolt catch and hold the bolt back?
 
dangertree said:
I missed this part in the first reading.
Not to be an ass, but did you double check the mags were fully seated?
Can you manually engage the bolt catch and hold the bolt back?
Click to expand...

Good point.

Many of the currently available pinned mags (limited to 5 rounds) are pinned so tight that they will not seat properly on a closed bolt. What you have described sounds a lot like a magazine which has not been seated properly.

Try inserting an empty mag and lock the bolt open by pulling the CH. Now insert a loaded mag and push the bolt release. Shoot.

This may well solve the problem, let us know.
 
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dangertree said:
I missed this part in the first reading.
Not to be an ass, but did you double check the mags were fully seated?
Can you manually engage the bolt catch and hold the bolt back?
Click to expand...

i did check that. i loaded the mag with only 1 round and its still the same. the bolt catch is fully functional when manually engaged.
 
Gothmog said:
Good point.

Many of the currently available pinned mags (limited to 5 rounds) are pinned so tight that they will not seat properly on a closed bolt. What you have described sounds a lot like a magazine which has not been seated properly.

Try inserting an empty mag and lock the bolt open by pulling the CH. Now insert a loaded mag and push the bolt release. Shoot.

This may well solve the problem, let us know.
Click to expand...

i think you have a very good point. i will try a bunch of diff mags next range outing
 
First off I hope you are nor running a LMT Enhanced Carrier. This will cause short stroking in a shorty . It can be identified with the 3 ( instead of the ususal 2 ) vents

Secondly LMT 10.5s are a bit more finicky when running anything other than NATO spec ammo due to the relatively smaller gas port size. See link to previous thread

http://www.canadiangunnutz.com/forum/showthread.php?t=284058

This compounded with the fact that your rifle is new , you shoud give it a little bit of time before you think you have a problem

Assuming you are NOT running a Enhanced carrier, I would suggested lube the carrier / bolt generously. This made a huge difference in mine.

Run at least 200 rds through it and it should be locking back fine on all mags

I had the same trouble with mine, especially with the Questar 10rd. The advice above was what LMT gave me when I called

BTW , if you want to do some reading, head over to m4carbine.net and search LMT 10.5 and you will find discussions regarding your problem

I highly doubt LMT would have a upper go out with a misaligned gas port, but if you are still having problems you should call them. They are very helpfull
 
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