What would cause an AR to stop cycling after 100 rounds?

[paulosantos]

I've been having problems with one of my AR's. After approximately 100 rounds, it just stops cycling. It will fire the round, but will not cycle the next round. It actually ejects the round, but it only ejects it about 1 or 2 feet away from the AR, instest of the usual, which is several feet to the 4 or five o'clock position. This has happened on two consecutive days.

Yesterday when it happened, one of the magazines was getting a little gouged on the right lip. Also, with the bolt locked to the rear, I put in a loaded magazine and released the bolt and it would not go all the way forward without using the forward assist. I initially thought it was not lubed enough since I used Slip2000 for the first time and I tought that had something to do with it, but last night I used CLP and it was well lubed today.

I think I ruled out any mag issues since I have used the same mags for a while and it does it to all the magazines. The AR was cleaned and lubed properly each time. The upper is a a Stag upper and it is a couple of months old. The Carrier is about 3 years old and has over 10,000 rounds through it and I check it and it looks good and the carrier key is on good. The bolt is a year old and has almost 10,000 rounds through it and it also looks good. I took the Troy Handguards off and checked the gas tube and gas block and they look good also, but I did not take them off.

Any sugestions before I send it out to get looked at? I know I'm all over the place, but I never had any problems like this before.

[Canonshooter]

I would start by looking for gas leaks; where the tube enters the FSB, make sure the carrier key is tight and check the rings on the bolt.

Edit - my bad, didn't read your post thoroughly enough. If closing the bolt won't chamber a round, it's something else. I'd look real closely at the BCG.

[paulosantos]

I would start by looking for gas leaks; where the tube enters the FSB, make sure the carrier key is tight and check the rings on the bolt.

Edit - my bad, didn't read your post thoroughly enough. If closing the bolt won't chamber a round, it's something else. I'd look real closely at the BCG.

I think that the BCG is one of the problems since it was so hard to chamber the round. I'll just have to send it to get it repaired since I broke the gas tube while trying to take it off to check the front. I should have just sent it out. Thanks for the help.

[120mm]

I've ruined enough gas tubes that I just replace it each time I work on it. It's cheap.

[onmilo]

+1 on the bolt carrier.
If the carrier key is feeding into the gas tube without binding chances are you have a misdimension in the bolt carrier.

Is it an 'AR15' bolt carrier that has been milled out on the bottom up by the firing pin?
I am certain these carriers cause more problems than they solve.

You certainly can't use one of these politically correct bolt carriers to convert a rifle to full auto.
Heck, most of them don't work correctly in semi-auto!

[paulosantos]

+1 on the bolt carrier.
If the carrier key is feeding into the gas tube without binding chances are you have a misdimension in the bolt carrier.

Is it an 'AR15' bolt carrier that has been milled out on the bottom up by the firing pin?
I am certain these carriers cause more problems than they solve.

You certainly can't use one of these politically correct bolt carriers to convert a rifle to full auto.
Heck, most of them don't work correctly in semi-auto!

I'm almost positive it was either the BCG or the bolt since something was rubbing pretty bad on the magazine lip. Either way, I'm getting a new BCG and bolt since they are very old and used anyway. Thanks for the help guys.