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Discussion Starter #1
Hey, I have a stock AR-15 manufactured by Colt. Rifle is not cycling through and chambering another round some times. I have no mods on the rifle. the rifle is clean.I have experiince in cleaning M-16's from time in USMC. Any ideas of what it could be?
- I have tried different magazines ( they fire well on another AR)
-I have used Federal ammunition ( no knock offs )
The problem usually shows up after firing part of one magazine. after that I am having to manually work the bolt to put another round in the chamber.
This is really frustrating.
 

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Troubleshooting an AR is one of those things that's gonna end up with 100 replies back and forth before you figure it out. ARs are pretty easy to figure out if you've got a second one or a friend with one to borrow. Swap upper and lowers, which one carries the issue? Upper, swap BCGs. Lower, swap buffer or springs. That kind of troubleshooting makes life a little easier.

That said, does the rifle extract the fired round? Have you used different kinds of ammo? Federal is decent ammo but maybe you got a bad lot. Different manufacturer magazines or trying several of the same? If it is extracting then the ammo may be too weak to push the bolt behind the next round on the mag. Maybe your mags aren't feeding properly. Could also be a gas leak where the key is mated to the BCG. How do the bolt's gas rings look?

Hope that is at least a decent start.
 

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If it's new, send it in for repair. If it's well used, could be a number of things from buffer spring, to a dirty bolt. But if it's going thru 1/2 a mag before it starts FTF, I'd think it needs a good cleaning for starters. Strip if down, clean it all, bcg, firing pin hole, gas block, etc.
If the bolt has alot of built-up carbon in it, it can interfere with ejections.
I know you said the mags were good, but try loading 15 rounds only, in each mag and see if they feed w/o a jam. If they don't jam, it's most likely weak springs.
And if you or someone else has ever fired "lacquer coated" steel casings, the breech may have enough residual lacquer in it to cause sticking when the chamber is heating up from firing. Clean it good.
I'm sure you have already cleaned it, and maybe everything, so this is a just in case reminder.
Other problems could be a weak buffer spring, ejector going bad/or carbon, weak mag spring, and as already stated, a gas leak.

g/l
 

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I have had this issue a few times. It's generally over-gassing.

Probably the gas port is too big. For some reason the industry likes to have overly large gas ports. Over-gassing is when the bolt unlocks prematurely when the pressures in the chamber are still high. So what happens is the BCG will cycle at a higher speed causing rounds not to be picked up or the BCG not locking back on an empty mag.

Does the BCG actually lock back when you fire the last round from a magazine?
 

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Discussion Starter #9
update to AR 15 issues

thanks for the input. I cleaned it thoroughly then went back today. I switched upper and lowers with another AR. No problems with the lower receiver. My upper receiver had the same issue. after firing a couple of rounds it failed. it was not ejecting a round and failed to feed a new round. When I used up the magazine the bolt did lock back.
 

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Was it failing to extract or was the brass extracting out of the chamber and failing to eject? Sounds like it has enough gas to cycle properly if it's locking back on the last round. Do you happen to have another bolt or BCG to swap?
 

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Before going forward on troubleshooting what rifle is it by colt?

Is it carbine, mid-length, or rifle gas system?
What buffer did they send with it?

Considering this is a factory rifle and assuming that it has the correct buffer with the correct gas system. It could be a few things on the failure to eject. The extractor spring could be weak or the rifle could be short stroking. If everything is to manufacturer specs I am willing to bet there is something that is miss aligned with the gas system. Probably the gas block.

If you can the next time you fire it have an individual take a video of you loading a 30 round mag into the rifle, shooting until it fails and post that video for us so we can watch it. This will help a lot for everyone trying to help troubleshoot the issue.
 

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Have you got this fixed yet? I have experience from 20 years in the army. My first question since you said it is stock, did you buy it new? Many different things can cause what you are describing.
How far is it ejecting when it fires normally? Short throw replace the ejector spring.
Check to make sure your gas key is tight and properly aligning with the gas tube.
If you didn’t buy it new, I would try different buffer springs and buffer. Some people try stronger springs and this can cause an issue. Make sure to stagger the gas rings on the bolt. Hope this helps.
 
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