Previously reliable AR suddenly not cycling.

**TF82** · 12-10-17, 12:52

Originally Posted by sig1473

Maybe it's just me, but I see no roll pin in your FSB. If the roll pin somehow fell out, your gas tube might have moved back a tad causing insufficient gas to cycle.

Yeah, it does look to be missing. If you don't have a gas tube roll pin, you'll want one.

**sig1473** · 12-10-17, 13:04

Originally Posted by Circle_10

There is a roll pin present, it just doesn't show up well in the pics.

Gotcha

**Circle_10** · 12-10-17, 13:55

I suppose I could also try sticking the bolt into another carrier and see if the gun will run like that.

**Todd.K** · 12-10-17, 15:04

Swap in a known good carrier.

**ST911** · 12-10-17, 15:25

Take the buffer and spring out, check the roll pin in the buffer and see if it's walking out and dragging on the spring.

**TomMcC** · 12-10-17, 15:58

Originally Posted by Circle_10

There is a roll pin present, it just doesn't show up well in the pics.

It doesn't appear particularly worn when compared to a couple spare BCM tubes I have on hand, a new one and one that had seen light use. Unfortunately those two are both carbine-length ones.

My best best seems like it might be to preemptively order a new gas tube and replace the one in the gun and clean the BCG etc off and perhaps try the thinner Slip 2000 vs the thicker EWL30.
This has been a really good gun up until this morning and I'd like to get back up and running again ASAP.

The end of the gas tube looks fine, and your oil isn't the problem. After checking the spring and buffer like ST1911 said, with the gun all back together, retract the bolt back and forth. Are you feeling any unusual mechanical interference?

**TomMcC** · 12-10-17, 16:06

Also you said you C/O the rings 200 rounds ago. I have had guns short stroke temporarily until I got them broke in. This hasn't happen every time, but it did happen.

**Circle_10** · 12-10-17, 16:58

Roll pin in the buffer isn't protruding and doesn't seem to be loose.

No interference that I can detect while hand-cycling the bolt. I can ride the charging handle and slowly ease the bolt home and it will still go into battery without issue.

I did brace myself for potential cycling issues right after changing the gas rings out, but it functioned fine. It seems odd that now after at least a couple hundred rounds that they would suddenly cause the gun to choke. Again it's not like I've been having intermittent short stroking that's been getting progressively worse. I went from 100% function to having to hand cycle every cartridge into the chamber within a matter of a few rounds.

I'm wondering if there's some obstruction in the gas key/carrier that I'm not seeing, however I was able to feed a twist-tie (I didn't have any pipe cleaners on hand) from the gas key down into the carrier, it's pretty flexible so anything offering resistance in there probably would have stopped it.

Could there be some sort of obstruction in the gas tube itself?