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Discussion Starter #1
Actually, I posted about this about a year ago and I have had very little time since then to go shooting and try to sort the problem out.

I have a Colt AR that is having bad stove-piping issues.
The rifle has probably several thousand rounds through it. Other than the gas rings, it has all original parts other than putting on a collapsible stock and a different grip.
I started with the simple stuff first.
First was VERY thorough cleaning and inspection of parts, then lubing according to the owners manual.
I tried several different mags including brand new ones, and I've tried different types and weights of ammo in both .223 and 5.56 .
I tried a different extractor and spring (not Colt brand, some other aftermarket brand, maybe DPMS). That did not help so I put the Colt extractor and spring back on.

This past Saturday, I finally had a free day so I spent about six hours at the range. I mentioned to the Rangemaster the problem I was having, so he spent a lot of time watching while I was shooting. One thing he pointed out was that at first, the empties were spitting out pretty far at about 3 o'clock. After several mags (yes, with at least two stovepipes per mag), the empties were landing MUCH closer at about 1 or 2 o'clock. Literally landing on the table maybe 18 inches or 2 feet from me.
He told me to talk to their gunsmith who happened to be there that day. He said the guy had taken the Colt armorers course at the factory, so he should be able to figure it out. I took the rifle to him and he completely broke it down and inspected it. The only thing he did not take out was the ejector. That, he said, felt like the right amount of spring tension and was sticking out where it should be. Said the rings looked good, extractor looked and felt right, gas key properly staked, no visible cracks anywhere, no carbon build-up anywhere. Sprayed brake cleaner down the gas tube and it ran out fine. Checked the buffer, tube and spring. Made sure the little hole at the end of the tube wasn't blocked. The only thing he did was to slightly stretch the buffer spring. I told him how the empties were ejecting strongly at first but weaker the more I shot. Seems like that would be a major clue, but he didn't really comment on possible reasons for that. I swapped him some .223 for some xm193 to try, but those failed on the second round.
I will try to mention anything else I noticed, even if it seems insignificant. Maybe it will provide a clue as to the problem. I will also try to post some pictures that may help you diagnose the problem.

In the first couple of mags fired, the stovepipes occurred towards the last rounds in the mags. In later mags, the failures happened earlier in the round count. Almost as if the hotter the rifle got, the sooner the stoppages.
On a couple of the failures, the empty would stovepipe, but there would be a fresh round almost chambered underneath it. I will post a picture of this.
Check out the picture of the deflector on the side of the receiver. You will see normal marks from empties hitting it about halfway up, but right where the deflector melds into the receiver, you will see a bright spot where the paint is missing completely. Seems like the empties should be hitting higher up. Maybe insignificant, maybe a clue?
Another picture shows the round that partially chambered under the last stovepipe. There is a scratch on the side, but since it is not a straight line, I wondered would that be from the extractor or more likely made by the spent round above it? There is also a very slight gouge or scrape on the TOP of the base of the round. You have to look close to see it. The bottom of the base looks normal. Again, maybe a clue?
One other thing. After stripping, cleaning and lubing the bolt and BCG, the bolt seems a little stiff going in and out of the BCG. You know how you can push the bolt in and then flick it out a quarter inch or so, it will do it but somehow it seems like its a little sticky flicking it out. That could just be my imagination since it's been so long since the rifle ran properly.
As mentioned, I replaced the original fixed stock with a collapsible one. It ran fine for a long time with only a very occasional problem.

I have scoured the internet trying to figure what else to do. At this point, the only things I can think of would be to replace the ejector and spring, and maybe the extractor and spring, this time using Colt parts. I've also read that maybe a heavier buffer might work. I've heard that slows the action down so maybe the empties need slightly more time to clear the chamber(?). Other than that, all I can think of is to ship it back to Colt and let them work on it.
I would appreciate any advice you guys can offer.
 

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It could be that gas is escaping past the gas block and you aren't getting enough pressure back through the gas tube.
 

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I don't know but I am going to throw out some ideas off the top of my head.

I'll start easy and work our way up.

Pull out the buffer spring and check to see that it is still within spec. Also a close inspection of the buffer itself paying attention to the nylon bushing behind the buffer. Take a good hard look at the tube look for things the spring or buffer could be hanging up on. Clean everything well even the inside of the tube and give it a little lube.

Now on to the bolt carrier.

Check that your gas block is tight. It should not move at all not even a wiggle. Take a pipe cleaner and some Hoppes #9 and run the pipe cleaner all the way through the gas block into the bolt housing. Look for excessive carbon build up. Also using a pair of needle nose pliers run a pipe cleaner up the gas tube. DO NOT loose the pipe cleaner inside the gas tube. Inspect the end of the gas tube and how it fits inside the gas block. Look for a good fit and evidence of wear inside the gas block and on the end of the gas tube.

You said the rings were not original. How well do they fit inside the bolt carrier? Inspect the inside of the bolt carrier housing for scoring or wear. Keep in mind that ARs like to run wet. Next time your at the range try a heavier bodied oil on the gas rings and bolt chamber.

Inspect the rails on the bolt carrier looking for anything that can hang up. Lube it good and slide in into the upper trying to feel for any sticky places the bolt carrier should move smoothly with no sticky points and it should be tight.

On to the bolt.

Pull the ejector pin and spring and verify that the spring is to spec. Look for wear on the ejector pin since you got the pin out run a pipe cleaner up inside the hole and clean the face of the bolt really well especially around the ejector pin hole. Look for cracks in the bolt around the hole where the locking pin sits. I have heard this is a common point of failure.

Gas tube.

Remove the hand guard and inspect the gas tube for dings or kinks. If you can take the gas tube off clean out the gas block under the front sight. Carefully see if you can get a bit of telephone wire through the gas tube. If you can then pull a tiny swatch through the tube soaked in Hoppes. I know that this is way beyond a normal cleaning but you did say the weapon had several thousand rounds through it.

If none of that helps see if you can find a friend willing to swap out his entire bolt carrier group and charging handle for a few mags. Colt is Mil-spec right? If the problem goes away then at least you know the issue is with the bolt carrier and not the upper or the gas tube.

Good luck and let us know how it goes.
 

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clean and inspect your gas tube

also, when you switched out the butt stock did you change the buffer and spring as well?

The A2 style stock uses a different spring and buffer and it will effect the cycling of the rifle
 

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I was going to say check the buffer weight. Some rifles do not like the typical buffer weight used for the configuration of that rifle.
 

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Discussion Starter #6
Thanks for the feedback guys.

I have not pulled the hand guards off yet to check the gas tube. That is probably the one thing that I had not thought to check! All the other little things mentioned have been checked and re-checked.
The buffer and spring were changed when I put the collapsible stock on it. As mentioned, I ran a lot of rounds through it after changing the stock, with few problems. Still, I will compare spring lengths and buffer weights from the originals to the replacements, and try swapping them next time I get to shoot. If that doesn't work, I will put the original stock, spring and weight back in just to see if that clears it up.
Again, thanks for taking the time to respond.

HK
 

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just a suggestion, OP

get on Amazon and buy anyone of Sweeny's books on the AR.
The man is a genius and really helps you understand the finer points of how these wonderful machines work
 

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Discussion Starter #8
Checked the gas tube and it was fine. Compared the original buffer and spring to the replacement. Obviously, I cant swap springs as the A-2 spring is longer, but the buffer itself feels slightly heavier so maybe I can try swapping that and see what happens.
 

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Is your gas key loose or your gas block out of alignment?. thats what it sounds like to me
 

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Discussion Starter #10 (Edited)
Helix - The gas key is staked firmly. As far as the gas block, I will re-check that. When I had the hand-guards off yesterday, everything looked right but it's worth taking a closer look. I tried to see if the front sight tower was loose by trying to move it either way but it was solid. Thanks.


edit: I figure if the sight tower isn't moving, then neither is the gas block.
 

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Discussion Starter #12
Hah! I forgot what I was supposed to be working on!
 

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The screws may be staked but they also can be broken. If one screw is broke the gas can blow by.
 

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Discussion Starter #14
Funny you mention that. Today,I was just talking to one of our bosses who is into shooting. He had that very thing happen on one of his AR's. I will be checking that tonight if I have a little time. Thanks
 

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Discussion Starter #15
Update-

I bought a new BCG (wanted an extra one anyway) and my problem is solved. Put the new one in and ran about 120 rounds through it with no problems. Thanks to all who responded.
 
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