I have a 10.5" LMT that has just began showing early signs of short stroking. I noticed a week ago while at the range that it began failing to lock the bolt to the rear when the last round on the mag was fired. I switched ammo and used XM193 on my first test mag and it ran 100%. Second mag was Remington .223 and it ran 100%.
The 3rd, 4th and 5th mag were all Remington .223 and all of them failed to lock the boltto the rear. I have used Remington .223 in the past with no problems.
My setup is as follows:
LMT 10.5" upper
LMT semi BCG
I’m running and H Buffer
Noveske KX3
How many rounds did fire before the short stroking started?
Any signs of gas leaking any more than usual at FSB does the end of the gas tube have normal even wear ?
Does the gas key look fine any gas leaks that you can see.
Does it fail to lock back the bolt on all the differant mags are does it only happen with one manufactures mag?
Also how much oil are you running on the BCG?
I replaced the gas rings on my second trip to the range. I was hoping that would be the problem since one of the original rings was a bit warped. I soaked this thing with CLP just before shooting.
I am honestly at a loss for what could be causing it.
LMTs are made to run on NATO powered ammo. Going less than that opens the door for these problems.
If the gun runs on NATO pressure ammo I would stick with that and change nothing.
If you really want to run SAAMI ammo you might want to try a standard CAR weight buffer.
LMT ships its complete factory 10.5" guns with a regular carbine buffer. Put one of those in instead of the H buffer. Also, I agree with the comments about using 5.56x45 ammo, not .223 SAAMI pressure ammo.
Run a carbine buffer and full power ammo. I bet it runs fine that way.
As noted above LMT 10.5s are designed around 5.56 ammo, and use of the CAR buffer. The gas ports on these are some of the smallest you will find on a short barrel.
I have one and had a ton of short-stroking problems with underpowered training ammo. I tried everything to make it work with this ammo (most of the ammo I shoot is GOV provided frangible, and I carry .223 LE rounds for work), and finally decided it was worth it to me to have the port enlarged a bit. I would not recommend it to everyone, it just depends on what ammo you will be shooting most.
There is nothing wrong with the guns, they are just ported for a specific ammo.
Using a factory LMT 10.5" barrel and going up just 2 thousands makes a pretty big difference for using .223 pressure ammo and either a CAR or H buffer. Numbered drills are your friend here.
As others have reported, LMTs have smaller gas ports than others. I haven’t verified this personally, but can tell you that I’ve had an MRP give some trouble short stroking with cheap ammo.
It ran fine with 5.56, so I simply created what I call my “wolf buffer spring”.
I clipped 1 turn off it at a time until the gun ran properly, then I degreased it and spraypainted it Yellow. Problem solved.
I’ve tested it with the short spring and the gun works fine with full power ammo but is certainly not optimized for it. (However its no worse than any other over-gassed gun out there) If I’m going to be shooting 5.56, I’ll spend the 90 seconds and switch out the spring.