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Discussion Starter · #1 ·
Ever since I sent my MCX in for the new BCG, I've been kicking myself. Before I sent it in it ran flawless, but since, I can't get thru a full magazine without multiple FTE. I've already sent it in once, and they said they replaced the gas block and ran three mags thru it with no problems. I had high hopes that they found the problem, BUT noooo. I went to the range yesterday, and it started again multiple FTE in the first magazine. I've tried different companies, different grains, different shooters, and still have FTE. So, I guess I get to send it back to Sig Sauer again. Is there anyone else who is having the same problem? I really enjoyed shooting it before the recall, but since not so much. I've tried different gas block settings, I've tried a POF roller cam pin, and still no good. With all that said, I also run it pretty wet. Does anybody have any suggestions?
 

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Sorry your rifle is having problems TC. Sounds like SIG's 1st effort was a 'swing-and-a-miss' too. It may help to take some pics of the failure condition to better understand exactly what's happening.

SIG replaced the gas valve, which may suggest they thought the gun was under gassed and short cycling. That seems very different than something related to the new Carriage Assembly that started your misery.

I mean, replacing the new bolt's extractor and spring would be a FTE repair that's related to the BCG...

I always run my MCX on it's low gas setting just to minimize wear. This rifle is totally reliable with both 5.56, 223, 300Blk supersonic unsuppressed and suppressed on this low gas setting. The only 'failure' it has is it doesn't lock back the bolt on an empty mag running this low gas with 300Blk unsuppressed. I don't consider this a failure, because the higher gas setting was designed for running 300Blk unsuppressed, and adverse/dirty conditions.

Anyway, get some good close ups of your gun's failures for the SIG folks to chew on, and give 'em another pitch.

Cheers
 

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Discussion Starter · #3 ·
Here's a couple of pictures that I have provided to Sig on the first time shipping it back. Plus, I also sent 4 Magpul mags that I use in this rifle, and the torn up casings.
 

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Ah - I see said the blind man!! Thanks for the pics.

Yeah, I can see why SIG's smith though she's under gassed. Since the bolt is in it's extended position, sure looks like the extraction portion of its cycle was too weak to completely eject the spent casing that was then rammed back into breech.

So, what else could interrupt her extraction cycle?

Does the gun hand cycle smoothly?

Is there any unusual wear inside the upper receiver or on the carriage assembly indicating something binding?

Are the carriage assembly parts at least lightly oiled?

Are the barrel positioning pins located fully into their mortised slots?

Is the off white, slim buffer pad installed in the back of the lower receiver? MCXs with those original reddish, thicker buffer pads will short stroke with these new carriage assemblies.

Cheers
 

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Discussion Starter · #5 ·
Ah - I see said the blind man!! Thanks for the pics.

Yeah, I can see why SIG's smith though she's under gassed. Since the bolt is in it's extended position, sure looks like the extraction portion of its cycle was too weak to completely eject the spent casing that was then rammed back into breech.

So, what else could interrupt her extraction cycle?

Does the gun hand cycle smoothly?

Is there any unusual wear inside the upper receiver or on the carriage assembly indicating something binding?

Are the carriage assembly parts at least lightly oiled?

Are the barrel positioning pins located fully into their mortised slots?

Is the off white, slim buffer pad installed in the back of the lower receiver? MCXs with those original reddish, thicker buffer pads will short stroke with these new carriage assemblies.

Cheers
Gun cycles fine by hand with no binding

No unusual wear inside of the rails, or on the BCG

BCG is well oiled

Barrel positioning pins are in correct location

It has off white slim buffer pad installed

O-ring is still in place on ejector

Hopefully they will just replace the BCG this time
 

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Discussion Starter · #6 ·
Almost seems like your not getting enough gas to kick it back to the ejector.

Have you tried to lube up the rails the springs ride on?
Lube the bcg rails?

I haven't looked in my mcx ejector, does it still have the o ring?

Anyways, this is why I am holding out on sending my perfectly functioning rifle in.
As long as you do not plan on ever shooting 300 blackout you'll be fine.

I wish I knew someone who lives near me that had a MCX so I could see how my BCG functions in their rifle, but no such luck.
 

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Almost seems like your not getting enough gas to kick it back to the ejector.

Have you tried to lube up the rails the springs ride on?
Lube the bcg rails?

I haven't looked in my mcx ejector, does it still have the o ring?

Anyways, this is why I am holding out on sending my perfectly functioning rifle in.


Yeah. I've pretty much given up on any plan to send in my BCG for replacement.
 

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I pulled that thing off. Haven't had any problems.
I don't use it either for 300BLK. But a carbine length gas system in 556, it will make ejection more reliable when the chamber gets dirty after several hundred rounds or is over-gassed. But no,it is not absolutely necessary.

You can look at your brass, your rims will have a rough burr on the edge if the extractor if it is slipping off the rims. If so it could be a rough chamber or week or worn extractor claw.
 

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Discussion Starter · #12 ·
Wonder what Sig is shooting when testing such that they can't replicate the problem?
They told me alot of different manufacturer brands. They asked me again what I was shooting, and I told them mostly American Eagle 556 Nato 55 grain. Before the recall, all I ever shot was 223 55 grain with absolutely no FTE. Now I can't shot anything without a FTE, different brands, different grains, different shooters.
 

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Discussion Starter · #13 ·
I'll be sending it back to Sig Sauer on Tuesday. Hopefully it won't take the three weeks it did last time. May be they will either replace the BCG or the rifle (not likely).
 
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