BCM 11.5 upper troubleshooting

[markm]

JUST went through this retardation with a buddy's gun. GET RID of the stupid E carrier. Problem solved. I believe even LMT acknowledges the stupid carrier is NOT for carbines shorter than 14.5.

Definitely dump any o rings or other plumbing devices in the trash too. That junk is 1990s misunderstanding of how to make a short gun run.

[Iraqgunz]

There is no special tool required to disassemble an extractor (you simply use the firing pin retaining pin to push out the extractor pin). The O-ring pops off and that's it. If that is too much, I suspect that they also won't be able to zero and shoot the weapon either.

The original just says standard bolt. I was just suggesting using a known good BCG as the quickest test. Some people don't have the skills or tools to take a bolt apart and swap out springs and o rings

[steyrman13]

There is no special tool required to disassemble an extractor (you simply use the firing pin retaining pin to push out the extractor pin). The O-ring pops off and that's it. If that is too much, I suspect that they also won't be able to zero and shoot the weapon either.

We are on the same page. I was speaking more to the skills. I would still say it is quicker to just slide a BCG in and test it first. Or even just swap bolts.

[JustDSM]

Lose the O-ring to begin. Make sure you are also lubing it good. I would possibly look at upgrading to the A5H3 buffer but it will run as is.

I'll be heading back to the range today with this easy change...

I would try a regular BCG as well. That would eliminate the enhanced carrier causing issues or not.

As per the many replies about this, it's something I'll look at, but before I pick up a standard auto carrier I'll work with the enhanced carrier for now since I have it for one. I'd have to buy an auto carrier.. When I spec'd the parts for this upper it was heavily influenced by the reviews of folks like Grant and IG and how this system works on a SBR using a variety of ammo in both suppressed and unsupressed applications. *Note: Issues were all being fired unsuppressed, I'll run it suppressed once I can iron out issues when firing without the can.

I agree they will work, but when having problems to lock back or fully extract and pick up the next round it sounds like it may not be getting enough pressure to push the BCG back far enough.
Using a standard known good BCG could at least narrow it down to the carrier/o-ring issue rather than buffer or has port/gas block.

This reply got me thinking. The malfunctions looked as if the casing was "slipping" or being ripped off the extractor. Initially I thought that I was looking at an over-gassing problem since it appeared that the BCG was potentially moving too quickly causing the issue. That quickly faded in theory of the extractor spring not being able to keep pace, but when I got home and cleaned things up, The extractor has the insert, spring, and at that time the o-ring. However, what was observed was the spent casing 3/4 of the way (give or take) extracted but the round being stripped from the magazine being fed up into the spent casing still occupying that real estate. It's clear the spent casing and extractor "went separate ways" and on the return trip the bolt picked up the next round. Just wanted to make sure everyone was clear on that. The rifle was getting enough gas to cycle the BCG. It RELIABLY locked back every time on empty mags.

If problems persist I'll go to a standard auto carrier, but I'm not convinced at this point the issue lies in the carrier. At this point I'm more suspect of the bolt/extractor. In regards to the gas block/port. I didn't feel the need to measure the port as BCM's reputation isn't one I would typically question. However in the event this can't be resolved I wouldn't be opposed to looking into this. Just for the sake of complete disclosure, the gas block is set screw, and is aligned with the dimple in the barrel. I confirmed it's orientation last night, and there was no evidence of gas leakage.

No such animal... Where did the bolt assembly and extractor spring come from? Always start your troubleshooting with the cheapest part first. In this case, the extractor spring and insert. If your using an o-ring and still getting FTE's, it's likely either the spring or the extractor.

The "Standard Bolt" that I referenced was more to indicate that it wasn't a LMT enhanced bolt. The bolt that is being used is from Rainier. This one to be exact: https://www.rainierarms.com/?page=sh...roduct_id=3315

"Miil-spec shot-peened, AR15/M16 9310 bolts. Manganese phosphate treated & MP inspected."

I also trust Rainier, but as previously mentioned I'm a little suspect on the extractor at this point.. I'm tempted at this point to get a BCM bolt and try that before eliminating the E-Carrier.

I had 2 FTE's with my 11.5 BCM on the first 100 rounds (PSA bcg, standard spring, no o-ring). They also happend near 60-80 round mark.

I then ordered the BCM upgraded extractor upgrade kit (spring, insert and o-ring).

I installed the upgraded spring w/o the o-ring.

Next 100 rounds no issues. I know 100 rounds isn't much, but I don't exspect anymore FTE's.

It happened more than twice. Towards the end of the session it was pretty much ever round. I called it quits when it was clear there was a problem that needed investigating.

Thanks for the input guys. I appreciate the feedback and will report back.

[steyrman13]

I'll be heading back to the range today with this easy change...



As per the many replies about this, it's something I'll look at, but before I pick up a standard auto carrier I'll work with the enhanced carrier for now since I have it for one. I'd have to buy an auto carrier.. When I spec'd the parts for this upper it was heavily influenced by the reviews of folks like Grant and IG and how this system works on a SBR using a variety of ammo in both suppressed and unsupressed applications. *Note: Issues were all being fired unsuppressed, I'll run it suppressed once I can iron out issues when firing without the can.



This reply got me thinking. The malfunctions looked as if the casing was "slipping" or being ripped off the extractor. Initially I thought that I was looking at an over-gassing problem since it appeared that the BCG was potentially moving too quickly causing the issue. That quickly faded in theory of the extractor spring not being able to keep pace, but when I got home and cleaned things up, The extractor has the insert, spring, and at that time the o-ring. However, what was observed was the spent casing 3/4 of the way (give or take) extracted but the round being stripped from the magazine being fed up into the spent casing still occupying that real estate. It's clear the spent casing and extractor "went separate ways" and on the return trip the bolt picked up the next round. Just wanted to make sure everyone was clear on that. The rifle was getting enough gas to cycle the BCG. It RELIABLY locked back every time on empty mags.

If problems persist I'll go to a standard auto carrier, but I'm not convinced at this point the issue lies in the carrier. At this point I'm more suspect of the bolt/extractor. In regards to the gas block/port. I didn't feel the need to measure the port as BCM's reputation isn't one I would typically question. However in the event this can't be resolved I wouldn't be opposed to looking into this. Just for the sake of complete disclosure, the gas block is set screw, and is aligned with the dimple in the barrel. I confirmed it's orientation last night, and there was no evidence of gas leakage.



"Miil-spec shot-peened, AR15/M16 9310 bolts. Manganese phosphate treated & MP inspected."

I also trust Rainier,

I guess I assumed with the setup you have it wouldn't be the only m4 you had where you could just swap BCG with one of your other ones. The swapping of BCG is the quickest way to troubleshoot without having to actually change or take apart configurations. The next quickest is removing to Oring. Sorry for the assumption

That bolt you refer to isn't really Milspec if it is 9310. I have seen mixed reviews of issues with the enhanced LmT bolt/carrier. IG and Grant seem to have good luck with them, but others have had issues like MarkM speaks about which is why I suggested the quickest test which would at least narrow it down to either the BCG or something with the rifle. Hopefully it's just the Oring. Staying tuned for updates.

[PatrioticDisorder]

I have seen mixed reviews of issues with the enhanced LmT bolt/carrier.

Might wanna read some more, several guys on here are reporting using the Gen2 LMT enhanced bolt with excellent results... Same can be said for the Gen4 & Gen5 carriers... If he's not getting enough gas the cause could be many, but having a mil-spec BCG to swap quickly could easily rule out the carrier and/or bolt.

[JR TACTICAL]

I would listen to IG on this, he just built me an 11.5 BCM upper and its an identical setup to what you are running, minus the blot and buffer. I have a BCM bolt and an A5H3 buffer in mine and I have put 300 rounds through mine without an issue and it's been a combination of XM193, some of my hand loads and wolf ammo.

I don't know what gen E carrier you are using but I have a gen 4 or 5 in mine. There is a good thread on here that will help you identify the carrier. Just use the search feature.

Get a good bolt and by good I'm mean a C158 bolt from a reputable company. I bet that would solve the problem.

[JustDSM]

I just got the carrier a month and a half ago directly from LMT, so I'd assume it's the latest generation offering. I'll have to search around to find the differences between generations to properly identify mine.

I've got a BCM bolt on the way.

[MistWolf]

...It's clear the spent casing and extractor "went separate ways" and on the return trip the bolt picked up the next round...It RELIABLY locked back every time on empty mags.

It is clear from the above statement that your problem lies with the extractor or possibly the ejector

[Iraqgunz]

I wouldn't recommend the enhanced carrier if I thought for a second that it wouldn't work. Not sure what markm's deal with it was, but I have put thousands of round through various uppers with it. We recently did a demo in GA for an agency with the SIONICS 11.5" and enhanced carrier and it also ran 100 percent.

My money is on that bolt.