my 2 cents:
1) ammo: some commercial ammo are not hot enough to cycle the weapon
2) gas key loose?
3) worn gas rings?
since you've already checked points 2 and 3 I'd say it's ammo fault even if they worked for you in the past.
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my 2 cents:
1) ammo: some commercial ammo are not hot enough to cycle the weapon
2) gas key loose?
3) worn gas rings?
since you've already checked points 2 and 3 I'd say it's ammo fault even if they worked for you in the past.
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.
I would also try a regular carbine buffer as well. I would then run all the various types of ammo you have and see what happens.
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.
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.
Just a thought.