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Old October 17, 2012, 01:23 PM   #1
Kansas Shooter
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"Customized" AR-15 BCG?

I hope I don't show complete ignorance in this post, but an operator induced anomily was pointed out to me with one of my AR-15's carrier. I went to a private shoot Saturday and noticed I had some short-stroking and double feeding issues with one of my rifles. The one in question is a Colt 6920 I bought at a gun show in 2004 or 2005. I don't know how many rounds it had through it before I bought it, but I have fired roughly 3,000 rds. since owning it. A few years ago it began short-stroking and the problem seemed to be solved after changing the gas rings on the bolt. Since then, I have noticed a few of the same issues but not as bad as I had Saturday. I couldn't seem to get through 10-15 rds. without problems. A friend who was there is a Class III dealer and when he looked at my carrier, asked where the rest of it was. As you will see from the pictures, it appears that someone had machined off the lower half of the back of it. The other 5.56 rifle I own is a Knight's Armament SR-15. I honestly have to say that I did not think anything was different about the carrier from my Colt since I knew the bolt on the KAC gun was proprietary, but I knew the carriers were the same.

My assumption is that the reduced weight of the BCG is causing it to cycle too fast and not going far enough in the buffer tube. Is that correct? The buffer is an older style "H"-buffer. Was this someone's idea of making a low mass carrier at home? Everything cycled well when I ran my friend's full-auto carrier from his M-16. Sorry for the link...could not upload picture to the message for some reason.

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Old October 18, 2012, 05:04 AM   #2
bejay
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apparently colt used alot of variations on there bolt carriers over the years but the carrier is probably how it came from the factory.
http://ar15.com/archive/topic.html?b=3&f=118&t=554891
if it cycled fine with the other bolt carrier group obviously something is wrong with yours might check the gas rings again and check the gas key could be loose or have a broken bolt.
more weight should slow down the action and actually be more likely to short stroke than the lighter carrier.
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Old October 18, 2012, 08:24 AM   #3
Kansas Shooter
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The picture in the link is exactly what I've got. I thought it was something done in a machine shop since I could see faint marks around the area in question.

I have notice my gas key has a little movement; rings should still be good after changing them about 1,000 rounds ago.

I had looked on the other website you referenced, but did not look hard enough. Thanks for the reply and for the link.

Marty

Last edited by Kansas Shooter; October 18, 2012 at 08:35 AM.
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Old October 18, 2012, 09:24 AM   #4
riggins_83
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Is your gas key staked properly? Any looseness in that can easily result in short stroking. Have it tightened and staked properly, you'll probably be back in business.
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Old October 18, 2012, 12:43 PM   #5
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Quote:
I have notice my gas key has a little movement
Ahem... what riggins said, and get yourself a new gas tube while your at it.

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Old October 18, 2012, 01:08 PM   #6
Kansas Shooter
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Quote:
Is your gas key staked properly?
I believed it to be, but the key has loosened a little over time. I will address this and have been thinking about a new gas tube too. After a friend saw that part of the carrier was missing at the back, I wonderd if that would contribute to my problems. After seeing the link bejay gave, I know my carrier is ok.

Appreciate the responses
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Old October 30, 2012, 08:15 AM   #7
BerdanSS
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A class II dealer didn't know that was a pretty common Colt "semi circle carrier"? It's made that way to completely defeat converting to full auto with a drop in device like a lighting link or something similar. It should cycle better/faster with a lighter carrier.

It "shouldn't" be giving you any issues because it was designed for your rifle..but stranger things have happened. There is a MASSIVE array of quality AUTO carriers out there from places like Rainier Arms and Bravo Company just to name two. But if you want a factory Colt Auto carrier, go to Specialized Armament. They have Colt FA carriers stripped with key for $100 (<EDIT> just looked at them from SAW, price went up to $125 ). Just pop in your bolt and guts from your other carrier and your GTG.

pretty unlikely, but there may an issue with your gas port as well (too small, severely carboned up, submerged in water and left to rust by previous owner.)

Last edited by BerdanSS; October 30, 2012 at 08:30 AM.
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Old October 30, 2012, 08:43 AM   #8
Kansas Shooter
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I was surprised the dealer made an issue of it too. I guess he isn't familiar with Colt carriers during the ban years (like me!)

I have yet to do it, but before I get a new carrier, I think I will try to re-stake my gas key. I might change my gas tube out also since the gun has so many rounds through it.

I'm familiar with the companies you mentioned and have done business with Bravo Co. before. If it comes to a new carrier and key, I'll do just that.

Thanks for the advice
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