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Old 11-15-2012, 20:32   #1
WoodenPlank
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Well, crap...

When I went shooting last week, my SBR starting short stroking for no discernible reason. Everything was relatively clean, well lubed, and it had never had problems before. Unfortunately, I had no spare parts or tolls with me, so I was kinda screwed on troubleshooting.

I took it home that night and cleaned the crap out of it, and relubed everything. Couldn't find any worn or busted parts, so I figured that maybe it was chamber filth from the steel cased Tula.

This week, I hit the range again - same problem. This time, I had spares. I swapped in a carbine buffer in place of the H2, no joy. Swapped out the BCM bolt carrier group for a crappy, worn out DPMS, and the gun ran.

Whut?

Dropped the H2 buffer back in, gun still ran.



So, I swapped the BCM bolt into the DPMS carrier, and vice-versa. BCM bolt + DPMS carrier, and it ran. BCM carrier with DPMS bolt, no joy.

When I got home tonight, I started going over the BCM carrier. No obvious burrs or bad spots inside the carrier, so I checked the gas key. The staking on the front screw looked a little weak, so I checked the screw. One tiny bit of pressure later, and the damn screw turned.

To quote one of my favorite TV shows - "Well THERE'S your problem!"

So, I tried to tighten the screw down more...

and more....

and more....

This damn thing is stripped!



I can't get the screw out because of the staking, but the staking wasn't enough to stop it from spinning.

Lesson learned - Even BCM can screw (heh) up every now and then. I've only had this BCG for about 6 months, and it's only seen about 500 rounds (work has been a ***** lately), so it's definitely not due to use or abuse. I've already got an email in to them, so I guess it's wait and see to find out what they are willing to do to fix it.

Second lesson learned - it doesn't hurt to double-check gas key screws, even on bolt carriers from higher end companies. Just because it LOOKS staked doesn't mean it's really secured.
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Last edited by WoodenPlank; 11-15-2012 at 20:35..
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Old 11-15-2012, 20:38   #2
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Well atleast you got the problem pinned down. Sucks that the BCM carrier failed, let us know how it works out with them.
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Old 11-15-2012, 20:40   #3
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The sky is falling?

But anyway, I had to replace a gas key when I dropped it (a BCG) on a cement floor. I used new bolts and rockset that came with my AAC suppressor mounts. The reason I bring this up, is my clumsiness has given me an opportunity to test this staking debate. I put a little over 500 rounds through so far with no malfunctions. I only wish I would have made witness marks to have definite proof of if the bolts were unscrewing.

You have any interest in testing an unstaked gas key? Or try DSArms "key lock" gas key? Or are you content with staking?
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Last edited by LA_357SIG; 11-15-2012 at 20:44.. Reason: it = BCG
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Old 11-15-2012, 20:46   #4
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The sky is falling?

But anyway, I had to replace a gas key when I dropped it (a BCG) on a cement floor. I used new bolts and rockset that came with my AAC suppressor mounts. The reason I bring this up, is my clumsiness has given me an opportunity to test this staking debate. I put a little over 500 rounds through so far with no malfunctions. I only wish I would have made witness marks to have definite proof of if the bolts were unscrewing.

You have any interest in testing an unstaked gas key? Or try DSArms "key lock" gas key? Or are you content with staking?

If it gets fixed on my dime/headache, it's getting done right, and done overboard. Fortunately, I'll be seeing just the man for the job next weekend.

Then again, I get the feeling that BCM will be making it right.
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Old 11-15-2012, 20:54   #5
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Interesting. Good information to know, just in case.
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Old 11-15-2012, 20:55   #6
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Is the hypothesis here that the screws stripped themselves in 500 rounds?

Or were they factory over torqued to begin with?

Was gas leaking out where the screws were supposed to be holding the gas key tight to the carrier?
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Old 11-15-2012, 20:57   #7
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I had a similar problem with my LMT SBR upper when I first got it and it gave me fits. When I finally broke down and called LMT the first question out of the tech's mouth was what weight buffer am I running? Well, an H2 of course...everyone knows you should run an H2 in a Carbine length gas system right? Nope. LMT drills their gas ports to cycle with a standard weight carbine buffer. So I replaced the H2 with a carbine weight buffer and the stupid thing has run like a champ ever since. Never skipped a beat.

When gas keys are staked and things aren't perfect its not unusual to break off the bolt close to the carrier or just under the bolt head. BCM bolt carrier groups are made by fallible people using imperfect materials. Like all mechanical parts they have a failure rate...
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Old 11-15-2012, 20:57   #8
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Is the hypothesis here that the screws stripped themselves in 500 rounds?

Or were they factory over torqued to begin with?

Was gas leaking out where the screws were supposed to be holding the gas key tight to the carrier?
Over-torqued, and the carrier threads or screw threads gradually gave way.

I couldn't find any sure marks to show it, but I'm assuming gas was leaking out from around the gas key and causing the short-stroking.
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Old 11-15-2012, 20:58   #9
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I'm sure BCM will make it right, and send you a new BCG.

Just goes to show even "high end" parts can have issues.
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Old 11-15-2012, 21:00   #10
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I had a similar problem with my LMT SBR upper when I first got it and it gave me fits. When I finally broke down and called LMT the first question out of the tech's mouth was what weight buffer am I running? Well, and H2 of course...everyone knows you should run an H2 in a Carbine length gas system right? Nope. LMT drills their gas ports to cycle with a standard weight carbine buffer. So I replaced the H2 with a carbine weight buffer and the stupid thing has run like a champ ever since. Never skipped a beat.
I've seen various reports on what runs best in the LMT SBR uppers. I run an H2 in mine since I shoot mostly 5.56.

In this case, though, the bad key meant the buffer didn't make a difference. I tried it with a C buffer, and no joy.
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Old 11-15-2012, 21:01   #11
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That sucks. I hope you get it fixed soon. I am sure that BCM will take good care of you. They will probably replace the whole carrier with a new one. I also hope that this problem is extremely rare. Just ordered my third BCM BCG last week.
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Old 11-15-2012, 21:04   #12
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That sucks. I hope you get it fixed soon. I am sure that BCM will take good care of you. They will probably replace the whole carrier with a new one. I also hope that this problem is extremely rare. Just ordered my third BCM BCG last week.
I have no doubt that it's a rare occurrence, honestly.
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Old 11-15-2012, 22:41   #13
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Originally Posted by WoodenPlank View Post
Over-torqued, and the carrier threads or screw threads gradually gave way.

I couldn't find any sure marks to show it, but I'm assuming gas was leaking out from around the gas key and causing the short-stroking.
It was obviously properly torqued as it was tested and inspected. BCM has the best quality control in the business. In addition, they use genuine buffalo fat as a rust preventing preservative. The failure could have only been caused by your wanton and reckless use of Slip 2000. BCM's website clearly states that the use of Slip 2000 voids any and all warranties because it reacts with the genuine buffalo fat to create an exothermic reaction which literally cooks the gas key bolts, evincing that they were properly staked and making them into a tender and delicious snack that can be enjoyed at the range with a little Hoppes # 9.

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Old 11-15-2012, 22:42   #14
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It was obviously properly torqued as it was tested and inspected. BCM has the best quality control in the business. In addition, they use genuine buffalo fat as a rust preventing preservative. The failure could have only been caused by your wanton and reckless use of Slip 2000. BCM's website clearly states that the use of Slip 2000 voids any and all warranties because it reacts with the genuine buffalo fat to create an exothermic reaction which literally cooks the gas key bolts, evincing that they were properly staked and making them into a tender and delicious snack that can be enjoyed at the range with a little Hoppes # 9.

You had me going for the first two sentences, actually.

After that, it all came off the rails.
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Old 11-15-2012, 22:46   #15
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Originally Posted by WoodenPlank View Post
I've seen various reports on what runs best in the LMT SBR uppers. I run an H2 in mine since I shoot mostly 5.56.


In this case, though, the bad key meant the buffer didn't make a difference. I tried it with a C buffer, and no joy.
Call LMT. They will tell you exactly what I said.

You may get away with it in some rifles or may not. But my guess would be you are running it on the edge of reliability and when things get dirty or close to being out of spec it adds up.

Maybe not. I could be wrong. Been wrong before.

Honestly, Your BCG should still run with one screw tight as the key should still be tight against the carrier. But again, maybe not.
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Old 11-15-2012, 22:48   #16
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Well I guess I can't say I've never heard of a BCM failure. Let us know how they handle it.
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Old 11-15-2012, 23:16   #17
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Call LMT. They will tell you exactly what I said.

You may get away with it in some rifles or may not. But my guess would be you are running it on the edge of reliability and when things get dirty or close to being out of spec it adds up.

Maybe not. I could be wrong. Been wrong before.

Honestly, Your BCG should still run with one screw tight as the key should still be tight against the carrier. But again, maybe not.
It's not running. I can't *feel* any play in the key, but it's definitely not running. Bolt moves, just refuses to feed or lock back on empty.

As for the LMT bit, I was already considering dropping it to a Carbine carrier as a test. Once I get the BCM carrier un-buggered, I still plan to try it. Until the carrier failure, though, it was running perfectly even on Tula .223 with an H2 buffer.

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Well I guess I can't say I've never heard of a BCM failure. Let us know how they handle it.
It's a first for me, too. Hoping to hear back from them by e-mail tomorrow.
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Old 11-16-2012, 10:17   #18
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Plank- can you give me some quick education on this. Do you think this is SBR specific? Or do you think it would have given way in any rifle? I am not to familiar with SBR.
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Old 11-16-2012, 10:29   #19
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It's not running. I can't *feel* any play in the key, but it's definitely not running. Bolt moves, just refuses to feed or lock back on empty.

As for the LMT bit, I was already considering dropping it to a Carbine carrier as a test. Once I get the BCM carrier un-buggered, I still plan to try it. Until the carrier failure, though, it was running perfectly even on Tula .223 with an H2 buffer.



It's a first for me, too. Hoping to hear back from them by e-mail tomorrow.
I have a factory 10.5" LMT. It has a semi auto carrier and a carbine buffer and is gassed to run in this configuration as per LMT. They say you might have issues with M16 bolt carriers and H/H2 buffers in their SBR uppers.
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Old 11-16-2012, 11:04   #20
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Recently installed fifty (50) LMT 10.5" barrels all with full auto carriers. All 50 run like a champ on standard H-Buffers. Indeed LMT designs the port size for this, however I will say that there are always anomalies and to run whatever works.
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