LMT 10.5" run with SAAMI spec ammo???

[ashooter]

I have a new 10.5" LMT upper with LMT lower I SBR'd and the damned thing will not run with SAAMI ammo. Been tried with 2 different lower and several different proven mags, but the only thing it seems to run with 100% is M855. Tried Fed AE 55gr, Blackhills blue box 68 and 75gr, and Hornady NATO pressure TAP 75gr and NONE of them will run.

Is this normal for a new 10.5" LMT upper?

[MFS1589]

I am going to go with no on this one. It should run with the ammo you mention. My 10.5 LMT runs on everything from Wolf, AE, Radway green, Malaysian, Federal, etc.

What happens with the "bad" ammo, FTF, FTE, etc?

[Steve_Morrison]

Pretty tough to diagnose from afar without any pertinent information...
Perhaps you could let us in on the type of problems you are having- does your upper :

-fail to lock?
-fail to feed?
-fail to chamber?
-fail to extract
-fail to eject?
-Doublefeed?
-fail to cycle?
-shortstroke?

Whose bolt group are you using?
Who assembled the upper?

[DocGKR]

No, it is NOT normal. Our 10.5" LMT's run 100% with both SAAMI and NATO FMJ and OTM loadings from quality manufacturers (Black Hills, Federal, Hornady, Lake City, Winchester).

[Robb Jensen]

Originally Posted by ashooter

I have a new 10.5" LMT upper with LMT lower I SBR'd and the damned thing will not run with SAAMI ammo. Been tried with 2 different lower and several different proven mags, but the only thing it seems to run with 100% is M855. Tried Fed AE 55gr, Blackhills blue box 68 and 75gr, and Hornady NATO pressure TAP 75gr and NONE of them will run.

Is this normal for a new 10.5" LMT upper?

What bolt carrier, what buffer are you using? What types of failures are you having?

I recommend a standard Colt, FN, CMT or LMT M16 carrier, MP tested bolt, Crane O-ring or MGI D-Fender, H2 buffer and Brownells chrome silicone standard power buffer spring. Also use good mags like C-Products, USGI mags with Magpul followers or HK mags.

My 10.3" LMT short barreled rifle has a CMT bolt, Colt M16 carrier, Wolff XP M4 extractor spring w/Crane O-ring, ISMI buffer spring and CMT H3 buffer and it'll run even on American Eagle 55gr .223 and weak Wolf 55gr .223 This barrel was a 14.5" LMT factory barrel that I had cut down to 10.3" and the gas port opened up by Randall Rausch at www.ar15barrels.com I also used my Ned Christiansen 5.56mm neck and throat chamber reamer on it which barely removed anything.

If you want to send me the entire upper and I'll see if I can make it work. (no charge other than return shipping).

[ashooter]

Specifics:

CMT M16 bolt/carrier group with G&R's Crane O-ring, LMT lower with LMT SOPMOD stock & receiver extension, ISMI buffer spring, H2 buffer, CMT std trigger group... All is brand-spankin new.

Symptoms are that it goes bang, and will usually extract/eject but not cycle a new round off the mag other than ocassionally with Hornady TAP. Out of approx 60 rds Fed AE 55gr, 20 rds Hornandy NATO spec 75gr TAP, and 20+ rds each of Black Hills blue box 75gr and 68gr, it cycled one round into the chamber after firing a total of maybe 10 times. NEVER cycled more than once after going bang. Load one rd into the mag and it will NOT lock open on the empty mag.

Used 3-4 different mags that work fine in two other AR's - LaBelles with magpul followers, and CProducts...

Acts like it is not getting enough gas to me, but I sent it back to the builder and he said it seems to work fine on the builder's LMT lower using M855... but not with Black Hills SAAMI spec. LMT says they won't warrant it for anything other than NATO (M855 or Mk262 I assume) ammo.

I've been advised to try swapping out the ISMI spring with the stock stainless spring that came in the upper, then if that doesn't work, swap the H2 for an H buffer. I'll advise when/if we get it sorted out.

The big surprise to me is that the red box TAP wouldn't cycle it. that's pretty hot stuff.

[Robb Jensen]

Try a standard CAR length buffer spring along with the H2 buffer. If you need on let me know I have one I can send you. If it doesn't work with that then it should go back to LMT.

[ashooter]

gotm4,

Thanks for the offer(s)! I will see what happens. Hopefully it's a combination of factors and not that the upper is some kind of lemon. The new ISMI spring is noticeably harder to cycle by hand than another one I have in another lower that has maybe 500 rds shot with it. I do have the stainless spring that came in the lower from LMT I can try. It's about 1.5-2 inches shorter than a new unused ISMI spring I have lying on the bench right next to it, so hopefully that will make it work.

[JohnN]

I had the same problem, change back to the original spring and it should work fine.

[C4IGrant]

I built this weapon and have it now. The weapon runs like a top with M855, H3 buffer and ISMI spring. The lower is mine and is how I run my 10.5 as well. When I switch to weaker ammo, the bolt will not lock back, but does cycle.

Just as an FYI to those that are unaware of this, if you buy a LMT 10.5 upper and it doesn't run with the ammo you like and you send it back to them to fix and they get it to run with mil-spec ball, they will send it back and advise you that it runs fine. Their opinion is that they build their guns to run mil-spec ammo and if it doesn't, then that is on the end user.


C4

[ashooter]

I don't hold it against you Grant! I've bought enough other stuff from you to know it's gotta be "just one of those things".

Let me know what happens when you try a std carbine spring and/or lighter buffer with the A2. I may still have to tinker with changing different variables after I get it back from you, but at least I'll know where to start.

[TimP]

When I first got my 10.5 LMT last month it did the same thing as you described. Turns out the bolt was out of spec. The bolt was dragging really bad on the top round in the magazine, causing the spent case to extract, and eject, but not feed a new round. A lil work with a lode stone, and all is well.

[WILDBILL]

Dumb Question, but what ammo is and isn't MIL SPEC ? I plan in the future to get a LMT 10.5 Upper,LMT FA boltcarrier group to go on my LMT lower.

[ashooter]

UPDATE: Grant (G&R Tactical for those of you who've been asleep) said he's going to start from scratch and send me a new LMT upper.

Now that is above and beyond the call of duty, considering LMT doesn't sound too interested in fixing this upper.

THANK YOU GRANT!!!

[C4IGrant]

Originally Posted by WILDBILL

Dumb Question, but what ammo is and isn't MIL SPEC ? I plan in the future to get a LMT 10.5 Upper,LMT FA boltcarrier group to go on my LMT lower.

Anything with a Military designator (M855, MK262, M193, etc).

When I build a LMT 10.5, I test fire it with M855 (which is all I shoot). The issue is that sometimes the uppers will not run with anything BUT mil-spec ammo and most customers don't shoot it.



C4

[C4IGrant]

Originally Posted by ashooter

UPDATE: Grant (G&R Tactical for those of you who've been asleep) said he's going to start from scratch and send me a new LMT upper.

Now that is above and beyond the call of duty, considering LMT doesn't sound too interested in fixing this upper.

THANK YOU GRANT!!!

Your welcome.



C4

[Aubrey]

Originally Posted by C4IGrant

...When I build a LMT 10.5...
C4

Grant,
I'm curious what constitutes "building" a LMT 10.5. Aren't these complete uppers?

[C4IGrant]

Originally Posted by Aubrey

Grant,
I'm curious what constitutes "building" a LMT 10.5. Aren't these complete uppers?

I took it all apart and put it back together.

I installed a LT 7.0 rail and a KX3.


C4

[docsprague]

I just got a LMT 10.5 as well. First time out it would only run on 5.56 pressure ammo( Lake City and WCC m193 and Hornady 5.56 Tap). And it occasionally had problems with it until I took out the H2 buffer. It would not run on the PMP 223 I had. Took it home clean and lube the bolt again. Took it out the next day and fired 20 rounds of 223AE and 20 rounds 223 S&B through it and both worked fine. I plan on putting the H2 back in and giving it a try as soon as we get warmer weather here in MO.

To the pros: How much of this problem could be just getting the gun broke in?

[mark5pt56]

Either I got lucky or I got a good one. Although I have a standard spring, the buffer is a 9mm and m16 carrier group. Runs 100% with everything shot so far, 55 BH sp, 55 gr fed 193 and AE 77 bh 855