LMT 10.5 inch Problems after PWS FSC 556 Install?

General Firearms NFA
1

Guys,

I have an LMT MRP with both 14.5 inch and 10.5 inch barrels. I have run about 2000 to 2500 rounds through this rifle (mostly in the 14.5 inch) without any problems or malfunctions whatsoever. I recently changed the Smith Vortex flash hiders that I have on both barrels to the PWS FSC 556. I have run the FSC 556 on the 14.5 inch for a while and have had no problems with it. Today, I went to the range with the 10.5 inch barrel with the FSC 556 for the first time. From the very first shot fired, I had double feeds and also failures to eject. Again, I had no problems with the 10.5 inch when it had the Smith Vortex on it. I tried multiple magazines by multiple manufacturers (PMag’s, Lancer’s and Tango Downs) and they all had the same effect, even with different ammunition. My question is, would the FSC 556 be causing the problems? They only thing that I could think of would be that the FSC 556 is not allowing enough back pressure to cycle the gun properly? I haven’t had much experience with SBR’s and this is my first. Being that this is the only change that I have made, this is the only thing that I can thing of. I bet the 10.5 hasn’t had 500 rounds through it, I have a dedicated bolt and carrier just for the 10.5 inch and I have been using the stock LMT buffer which is I believe an H. I swapped back to the Vortex on the 10.5 inch when I got home, I just haven’t been back to the range yet. Do I need to run an H2 buffer if I plan on using the FSC 556 on the 10.5? Any help or info would be greatly appreciated.

Thanks,

Ben

2

I just went out to the range and ran 40 rounds through it with two PMag 20’s using XM193 and the Smith Vortex. I had a failure to eject after the first round fired. I cleared it, ran the remaining 19 rounds rapid fire. Did a quick reload and fired the remaining 20 rounds rapid fire with no problems? Got me, anybody have any ideas? Also, I examined all of the empty casings and they all had a fairly heavy dent or crease on the side of the casing, about mid way down the cae body? I don’t know if that would mean anything?

Thanks!

3

What brand bolt carrier group?

4

LMT bolt and bolt carrier that I purchased with the barrel a few years ago.

5

I’d replace this with a Colt unit and see what happens.

I also think you are in the “trinket” category with your flash hider decisions. I would not spend close to $175 on flash hiders when other parts of your gun are substandard.

6

Maybe I missed something but the PWS comp in not 175$, and LMT is not substandard.

7

WTF? this is horrible advice, scotty.

OP- what buffer weight are you using? sounds like the weapon was probably borderline over-gassed to begin with, and the FSCs creating just enough back-pressure to push it over the edge…

8

A PWS costs close to $100 plus shipping and the vortex is like $55 plus shipping.

And an LMT is certainly substandard compared to Colt in the stock hardware and BCG with MIM gas key issues.

9

How is it horrible advice?

When some off brand AR15 comes across my path that doesn’t work and I gut it and replace parts with Colt and it works, how is that bad?

10

because you can gut a Colt thats not working right and fill it with LMT parts and it’s just as likely to work right.

you’re a purist, and i respect that… but claiming LMT is “sub-standard” is bullshit. the INDUSTRY standard is far below what LMT is doing.

11

I can guarantee you with 90% certainty that if the BCG, buffer, and spring was replaced with Colt in the OPs rifle, the rifle would work.

My new way of fixing ARs hardly ever fails.

I quit trying to chase around chronic problems with aftermarket stuff and trips to the range for testing and just replaced the stuff with USGI and move on.

You guys can do what you want.

12

I have been utterly unsatisfied with my half dozen LMT uppers and LMT customer service’s response to issues with an LMT upper.

10.5s are sketchy to begin with, an LMT 10.5 (yes, I’ve owned one) is double sketchy.

My solution would involve dumping the entire upper for a quality 11.5" upper. I am partial to BCM for that.

13

i’m finding it difficult to accept this post at face value. mind elaborating a bit?

14

They refused to even look at the upper unless it had been purchased directly from a dealer.

15

Most likely an extractor issue given the type three malfunctions you’re getting (double feeds)… what buffer are you using? Meaning change out the extractor spring and possibly the extractor itself. Or replace the bolt (meaning you get a new extractor and spring).

Regarding changing to Colt, it has nothing to do with it being Colt v. LMT v. anybody else… rather it has to do with choosing quality over hit-and-miss quality.

16

If OP purchased the BCG a couple of years ago, the so called MIM issue may not be a problem for him. Or anyone else for that matter. Save the errornet hype for TOS.

17

I would try an H2 buffer.

18

Thanks guys! Wow, I didn’t expect all of this, which is fine though, gets guys thinking. As far as my BCG, it was purchased before the MIM gas keys and the BCG was purchased new and only has about 300-400 rounds through it, so I can’t see that it’s a BCG or extractor issue. I have already ordered an H2 buffer to give it a try. I agree with bkb0000 that the rifle was probably borderline to begin with and the FSC556 just pushed it over the edge. For what it’s worth, I LOVE my MRP and wouldn’t give it up for anyhing! With the 14.5 inch barrel, which is how I run it 99.99% of the time, runs like a sewing machine. I’m sure that it’is something simple, I just needed some help with diagnosing since this is my first SBR. I have a spare extractor spring kit that I will try also.

Thanks guys

19

I still wouldn’t trust it.

20

Swapping out the carrier with a known good one is one of the first things to do when trouble shooting.

Even a Colt carrier can have one of the carrier key bolts fail and being properly staked makes it very hard to see.