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What went wrong?






jimf5

Member
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2019 Supporter
#1
I had trouble with a new pistol upper not ejecting the shell and put it aside until i could get home and check it out. Got home and cleaned all the guns i brought to shoot and took the upper apart. It came out in three pieces, the charging handle, the BCG, and the top of the BCG yes i mean the part with the staked allen screws. the head of one of the screws was missing and the other was sheared off mid length. I attached pics to show what happened,anyone had this mishap?


20200331_133731.jpg 20200331_133716.jpg 20200331_133745.jpg

Jimf5
In Pahrump
 

42tula

uber Member
#2
Never had it personally, maybe the Allen screws weren’t the best grade material or over torqued? Who is the bcg manufacturer?
 

Janizary

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#3
I've seen improperly-torqued gas key bolts get sheared, but in both cases they were sheared evenly.

Same question as 42tula as well.
 

jimf5

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2019 Supporter
#4
I do not remember where i got the carrier. I just took it out of one of my other builds.

jim
 

MAC702

LEGEN...wait for it... DARY!
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#5
Start with what brand and model upper this was. Is it blowback or gas-driven? (At the time I asked that I was assuming a pistol caliber for some reason, and now note we don't even know what chambering this is yet.)

What is its previous history of reliability?

ALWAYS tell us what ammo you were using.

You say "not ejecting the shell." Was it cycling at all? Partially? Or acting like a bolt-action?

Additionally, the gun and rough description of the problem should be in the subject line so we remember what this thread is and can find it later.
 
Last edited:

Janizary

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#8
You say "not ejecting the shell." Was it cycling at all? Partially? Or acting like a bolt-action?
Yeah, I was wondering about that as well. Is it not extracting at all, or just failing to cycle enough to eject the round?

It looks like the carbon pattern might indicate that the front bolt wasn't tightened all the way down (or backed out a bit, like djthumper surmises). If the front of the key was lifting, even a hair, gas would leak perhaps not giving enough to cycle the carrier. Be curious to see if there was a carbon line inside the receiver, roughly where the key meets the carrier.

The front not being fully secure could account for the uneven shearing.
 

jimf5

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2019 Supporter
#9
Hi All :
A little more info. I pull the trigger, it fires , pull trigger again, nothing, drop the mag, round ejects unfired, put away for further evaluation this happend several times. I now know where the top of the front allen screw head went as i just noticed the dust cover is missing and must have been blown off when the top let go. I looked at the BCG and it has a logo but a search of all the places i buy from produced no results. I will check all my other AR's to see if i have any more with the same logo.
Will update with more info as i find it.
jimf5
 

jimf5

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2019 Supporter
#12
Hi all
I thought i had another BCG and i found it in another AR. I think i found the cause of my problem. The allen bolts were not staked properly. I took the proper size allan wrench and without much pressure they broke loose and i could barely feel the stake. Enclosed pic is just as i found the BCG taken from the rifle.

20200401_095200.jpg
 

Janizary

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#14
Glad you found that. I was looking around everywhere. I knew I had seen it before.
 

4x4Brit

Worktruck Driver
#16
Thanks for the help. I called the place i bought them from and they said they would take care of the problem.Already got a return label.
jimf5
in Pahrump
Always nice when issues get taken care of easily. Glad it worked out for you. Hopefully they stake the carrier screws a bit better this time.
 

jimf5

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#17
Thanks again for the help. The parts are on there way to So. Cal and should be delivered Friday. I will update when everything comes back.
jimf5
 

jimf5

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2019 Supporter
#18
Hi All:
Just a little update. They had both my bolts for 5 working days so i call for a status report and they will be sending two new BCG's today (Friday) and i got a tracking number. When they get here and the shooting area dries out will test them and report on the findings.
jimf5
 

jimf5

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2019 Supporter
#20
Yes i did inspect all the guns the bolts were in. The only damage was to the pistol upper with a few dings and the door blown off when the front bolt head flew out. The guns and especially ME were lucky more damage was not done .
jimf5