Newly built AR pistol feed issue

[Lennyjoe]

Not sure if this goes here or in auto loader forum but since we are talking about AR's I figured I'd go here.

So I put together my first AR pistol and thought I'd try a pigtail gas tube. Needless to say the gun didn't like it at all. Wouldn't even cycle the shot case out of a 7 1/2" barrel so I went to an adjustable gas block and a pistol length gas tube.

The trip to the range resulted in about 4 put of 30 rounds where the expended case wasn't thrown out all the way before the bolt picked up a new round. So, it seems like I need to adjust the gas cause I'm thinking I may be over gassed.

Sound about right?

 

[[email protected]]

First question is this with reloads or factory? Second question is what barrel do you have? I finished my first ar pistol build last month and I had similar problems. My barrel is an AR stoner from midway with a new full auto bolt carrier group. I cleaned the barrel with a chamber brush and solvent. It did fine for the first twenty or so rounds (its hard to shoot it without grinning). Then I started having problems. The spent case would leave the chamber but not eject from the upper. My first thought was that its undergassed and the carrier was not fully cycling. The ejector was ok. I tried some different loads with no change. I tried a semi auto carrier and a different buffer spring with no change. I could clean the chamber and it would do fine for about fifteen to twenty rounds. After alot of tinkering and inspecting I found out that the chamber was coated with the same stuff that the outside of the barrel was. This was causing too much drag for the extractor to hold onto the case, but enough to extract it from the chamber. This left the round loose in the upper. Check your chamber.

 

[Theohazard]

You might have an issue with the chamber like [email protected] said, but usually when an AR is leaving empties in the chamber it's due to being over-gassed; it's trying to unlock and extract the case when the chamber pressure is still really high and the case is still expanded and sealed into the chamber.

The most common fix for an over-gassed AR is to install a heavier buffer. This will keep the breech closed longer and allow pressure to drop before the case starts to be extracted, giving you smoother extraction/ejection and proper functioning. But if you have an adjustable gas block it's a lot simpler to just turn down the gas a little.

 

[[email protected]]

I read " the expended case wasn't thrown out all the way before the bolt picked up a new round" as the case was leaving the chamber. Can the OP clear this up?

 

[Lennyjoe]

The cases never left the upper. They were stuck almost vertical like the bolt moved too fast to fully eject the case and the new round was directly below. I'm definitely thinking its over gassed.

The barrel is an AR Stoner, all scrubbed clean and the BCG is a new WFA group. Finally, the ammo are my standard 55 gr reloads over H335 that shoots great out of my 4 other .223 AR's.

 

[[email protected]]

How well does an unfired round slide out of the chamber when its pressed in with hand pressure (see plunk test)? Mine would stick a little after firing a few rounds, but would drop out freely after I cleaned it lightly. We have the same barrel and my problem was that the chamber had a coating on it like the outside of the barrel. This increased the extraction force used. The case would extract enough to only clear the chamber. Try adjusting the block since you aready have an adjustable block, This may slow the BCG down enough for it to work, But remember what happened to it with the pigtail gas tube.Inspect the chamber really close and make sure its not coated.

 

[Lennyjoe]

Will do. I scrubbed the hell out of it when I first got it. Never like putting a barrel in without a close inspection, major scrubbing, and borescope inspection.

 

[rodinal220]

What type of buffer are you running?

 

[[email protected]]

I forgot to add that when I closely inspected the spent cases, I noticed little dimples on the brass. I suspect that after a good scrubbing of the chamber I started to get the coating loose causing the dimples. The dimples didnt appear on the brass until I started scrubbing the ever LIVING he-- out of the chamber. somtimes just scrubbing the he-- out of it isn't enough. I also missed it during the initial inspection.
I took a chamber brush chucked in a drill and spun it in the chamber with oil on the bruse. I then polished it. I dont like the idea of spinning a brush in the chamber but I knew in my case that I had a finish in the chamber that needed removed. Yours may be different so go easy on it.