I have a LMT defender that is having issues short stroking steel cased ammo. The rifle runs fine using brass factory loads. I have been having the short stroking issues with Silver Bear, Brown Bear and Wolf MC ammo (FMJ and HP). I have also tried several different mags (Pmags, L5's and USGI's). I put a lot of brass through this rifle with no issues and was planning to use it for competition but with the round counts so high for these matches it's a big deal on my end not being able to run steel cased ammo.

The rifle will always eject the spent casing and either do one of two things,

-it will go back fully into battery, failing to pick up and chamber and new round resulting in a "click"

-it will push the next round in the magazine a third of the way out and stop with the bolt sitting on top on the round.

I'm guessing this is a gas issue and was thinking of having an adjustable gas block installed by ADCO but I wanted to ask the experts on any problem shooting steps that could be taken to resolve this issue. I have heard that even a slight misalignment of the gas tube can cause SS issues, maybe that's the case? No idea?

The rifle is fairly new with less than 1700 rounds down the pipe, bolt carrier looks good, gas rings are fine and everything feels smooth while hand cycling the action with no binding to speak of. The rifle runs a standard carbine buffer and spring. The ejection pattern is pretty consistent also, ejecting cases to the 3 o'clock - 330 while using steel case.

Before anyone chimes in with "don't shoot junk steel case ammo", this is my main go to AR and I expect it to cycle any ammo I feed it. If my DPMS can cycle steel case without a hitch I would expect my LMT to do the same.

Any suggestions would be much appreciated.

Sounds like underpowered ammo. You can try a lighter buffer and see if that solves the problem.

Is there anything lighter than a standard carbine buffer?

LMT has had some issues in the past with under-sized gas ports on some of their bbls, albeit namely on their 10.5". Perhaps this is just a lemon?

Not that I know of (unless you consider the ultra rare carbine Edgewater buffer ).

It could be a case of an undersized gas port as the poster above me suggested.

Hope you get this sorted out, man.

Just a heads up that not all matches allow the use of steel-cased ammo.  More specifically, if the bullet is attracted by a magnet, it is potentially a no go.  Check with your match director.

My LMT was short stroking on some of the brass cased monarch (academy sports brand ammo) but it ran brown bear just fine for me with an H buffer. sounds like yours might be a little bit smaller than mine.

get quality ammo and see if it still short stroke....it's quite common with russian stuff

Do not go to a lighter than standard buffer.  It will cause the bolt to travel rearward faster than it should, and can cause damage or malfunctions.  It caused mine to double, and misfeed.  I rep[laced it with a standard, and all was well.

It's not so much that LMT has an undersized gas port as much as it is many brands having an oversized gas port that will run the lower powered steel case ammo. Have your gas port opened up if you want to run the cheaper ammo.

I had that problem develop all of a sudden with one of my rifles.  Check the bolt/carrier group and make sure that the bolt (rings) aren't binding in the carrier.  I still don't know what happened.  I just cleaned the bolt carrier really good and lubed it and put it together and it ran fine again.  Something in the carrier was causing the rings to bind up.

Other than that, check the usualy suspects.  Too much gas leasing from around the gas block/gas tube.  Check the gas key to make sure it's tight.  Check your rings to make sure they don't need replacing.  My last set of BCM rings only lasted 400 rounds before they wouldn't support the weight of the carrier.

When was the last time you cleaned your chamber?
As a note its adviseable to clean the chamber before switching from steel to brass cased ammo.Typically I'd recommend the chamber be cleaned every 400 rounds when firing steel cased ammo...at least thats my personal experience over the last ten years of shooting steel ammo.
One other issue is the red case mouth/bullet sealer Barnaul uses....it builds up and gums the throat of the chamber and is a PIA to remove.Wolf dropped the red case moutth sealer in the black box ammo a number of years ago due to the issue and it was well documented at the time.
I would also recommend a good lube and applied to the BCG in a nice sheen to keep things working well.

I always clean the chamber well with a chamber brush after every outing with the rifle in question. Out of all the guns I own the LMT is always cleaned imaculatly, second only to my daily carry piece. The rifle is always lubed correctly after a cleaning and before a shooting session.

Thanks for all the suggestions guys but I am really stumped as to what could be causing this malfunction other than the gas port either not being aligned properly or possibly having to send it to ADCO to get opened up a tad.

I have a one piece gas ring around somewhere. I think maybe I'll throw that in tonight and see if it possibly will help me out with the SS problem.

Any other idea's are more than welcome!

Side note: Does ADCO ever answer their phone? I always get the machine

I would not send it to ADCO(no disrespect intended)for modification.If you think there is an issue then the rifle needs to be sent back to LMT.

I would try an H buffer and better buffer spring, that is would I did with 2 of my M4s I used Spikes ST-T2 buffer and Spingco Springs and lubed them with Militec lube and oil, and shot over 1000+ of Steel Wolf with no malfunctions.

I was thinking of contacting LMT about the issue but I am afraid the conversation will go as follows:

Me - "My LMT is having short stroking issues with certain ammo types"

LMT - "What ammo are you using that is working, what ammo are you using that is causing short stroking"

Me - "Rifle runs fine with brass factory loads, it's short stroking with russian steel cased ammo"

LMT - "Don't shoot steel case ammo in your rifle"

Not really what I want to hear. Some people are fine with not shooting steel cased ammo but as much as I shoot these days it's unacceptable for my rifle not to eat and spit out Silver and Brown Bear ammo.

Well,I would not jump to conclusions.You dont know what they will say unless you ask.It would be worth the effort to at least let them to check the gas port diameter and that it has the proper location.If you have any modifications done to the gas port by an outside source,LMT will almost certainly say tuff titty if there is a future complaint as it will void the warranty on the barrel....if that concerns you any.
I run Wolf(to include some old laquer coated black box 62gr.FMJ from 2004) in my Defender without issue using a H buffer.Have from day one.So thats what I base my thoughts on in regards to your issues.I'd call LMT and talk with them at a very minimum.

You may have just got some weak ammo,so try a newer lot#.
This is kinda like trying to work the weapons function around crappy mags.It either runs or try something else.

Spoke with an LMT production rep this morning and the conversation went as I was thinking. The rep basically told me opening up the gas port a small amount would almost certainly fix my issue and allow me to cycle low powered ammo. He also said its a common issue they deal with but it's what comes along with the specs that they drill the gas ports to. The rep was very nice and courteous and added that any mod to the gas port size would more than certainly void any warranty associated with the upper receiver.

I have a couple more things I am going to try, swapping out the buffer and spring with another AR or maybe trying another BCG. If that doesn't work I may be sending this one out to get that gas port opened a very small amount afterall.

Thanks for all the suggestions and advice, much appreciated as always

I purchased a couple of boxes of Wolf Mil Classic just to try it out & shot it through my LMT 14.5 a while back. It short stroked with each round in the LMT but shot fine in my other ARs. I just figured it was the gas port on the LMT & left it at that. I've always been a brass cased US manufacture ammo anyway.

Are they willing to open it up for you to maintain the factory warranty?

I am with you on that, I maintain a healthy stash of US manufactured brass cased ammo always but as I stated earlier, shooting the cheap russian stuff gets me more time behind the gun more often.



No they will not alter the gas port from it's current Mil-spec diameter.

Gas leak around the FSB?  Carrier Key?  Gas Rings worn out?  Gas Tube worn out where it meets the key?

The carrier key is properly staked and is firmly attached, gas rings and gas tube are GTG. I don't think there is a gas leak around the FSB, I don't notice and excess fouling in that area that would indicated a leak.