Educate me please....question about SBR and BCG.

AR/M4 AR Technical Discussion
1

I have an 11.5 inch SBR I recently put together that I am having gassing problems with.

I am using an 11.5 inch Noveske barrel, H2 buffer and the only extra BCG I had laying around…an LMT Enhanced Bolt Carrier with their Enhanced bolt as well.

The gun runs fine either suppressed or non suppressed except it will not lock back on the last round.

I pulled a Young NM BCG out of another rifle and it works fine.

I swap the bolt out of the LMT Enhanced carrier with a standard bolt (in place of the LMT Enhanced bolt) and it runs fine.

So obviously the bolt is the problem. Its my understanding that the LMT Enhanced bolt was meant to run with a 14.5 inch barrel anyways.

So here is my question, the BCG is one that I had pulled from a 14.5 Noveske that I sold. I had around 500 rounds fired through it at the time. I have a brand new MPI tested bolt that I bought from BCM that I tried in the LMT carrier that runs fine.

Is there a problem throwing a new bolt in the mix now and with that carrier? It doesnt seem like 500 rounds would be enough to create any wear patterns that would cause excessive wear problems with a new bolt…but I figured I would check opinions here before i went out and ran it hard with the new bolt.

Or would I be better off just buying a new standard BCG?

I was just trying to save a few bucks and use parts I already have but if I need to Ill just scrap the idea and buy a new bolt.

2

All you need is to add an H3 buffer and possibly a blue Springco spring and you should be good to go. My BCM 11.5 did the same thing and once I added an H3 and Springco I was good to go.

3

I’d ditch that bolt anyway… Even if you up the buffer system.

4

I was thinking that. So no problems throwing a new bolt in a bolt carrier with about 500 rounds through it?

5

I have heard great things/plan on getting an enhanced carrier for my suppressed build but does anyone use and like their enhanced bolts? Non-standard extractors make me nervous :fie:

6

The BCG ran fine in my 14.5 inch gun…never a problem. But I did only have 500 rounds through it, not exactly a torture test.

7

I wouldn’t see a problem with it, just run the standard checks after its re-assembled.

8

The enhanced carrier was designed for 14.5"-16" carbine gas barrels.

9

So why does the bolt affect function? The carrier works perfect with a different bolt.

10

Not sure, I’m just going off what I know of the enhanced carrier and what LMT recommends it be used in.

11

I don’t believe the bolt does. I believe it was a fluke. In any case I believe that if you simply put an H3 in and a Springco spring you will be good to go.

Of you can install an A5.

12

No idea, I thought the enhanced bolts only differences were pertaining to the improved extractor. Looks like an e3 bolt to me…

credit to MilitaryMorons:

13

OK, thanks for the info guys.

Looks like an H3 and new spring are in order. Ill get them ordered today and report back when I test them out.

14

I think this has more to do with the bolt than the carrier. The carrier is designed to help 14.5" and BELOW guns.

The enhanced bolt needs to be used with 14.5" and ABOVE lengths.

I have been running an enhanced carrier in my 10.5 forever.

To the OP, get rid of the enhanced bolt for your SBR.

C4

15

HIJACK: I am currently building my SBR…the lower anyway. Going with a Noveske 10.5" MK18 upper. Is it pretty common to need the heavier buffer and spring?

16

OK, help me understand this real quick.

An H3 buffer is the heaviest right? So wouldnt a heavier buffer cause it to short stroke… exacerbating the problem? Or does a heavy buffer add to reciprocating mass and allow the bolt to travel further back against the buffer spring?

Anyways, heres a crappy cell phone pic of the culprit.

17

Weren’t you the gent that had that big long thread about suppressed SBR’s? I figured you’d have some experience with it.

18

I believe that if you read that thread, Grant used only the carrier and not the bolt. I may be wrong.

In any case I have made my recommendation. It’s up to you to drink the water or look for another well.

19

Yep.

C4

20

No, I gocha…I appreciate the input. Im just trying to understand the mechanical function of it a bit better.

It would seem to me a heavier buffer would make it short stroke no?