AR Pistol Trouble Shooting

[democracywins]

I recently built my first AR pistol after building probably two dozen or so rifle length AR15s. And I'm having a issue. The gun won't cycle certain magazines and it is inconsistent on magazines, it is not just one kind or another. When it fails, it will fire the round and eject but fail to feed the next round. My first belief was a mag issue, but it is doing it on mags that I turned around and cycled fine through any of my rifles I grabbed after it failed in the pistol. Then there are magazines that it will run an entire mag with no issue. My thought is that I need a strong buffer spring or a problem with the gas tube. Any thoughts or advice would be appreciated.

 

[Manatee]

Buffer spring might be too strong or buffer weight might need to be changed. Gas tube alignment or port size might need to be looked at.

 

[Ljungman]

AR pistols are touchy as all get out about their gas systems, and spring tensions/weights. Make absolutely sure you got a pistol barrel that had its gas port drilled properly, your gas system is aligned properly, and check to see if your spring can be changed out for a weaker one. that symptom is usually a sign of not enough gas to push bolt all the way back to clear the cartridges in the mag while able to kick fired brass out. Other wise on a less frequently seen note....take a dye marker and rub your bolt carrier down and see where it rubs inside of the upper. if your upper isnt 100% true it may be causing unneeded friction to the carrier slowing its rearward travel causing a "short stroke" situation that you are describing. also check the bolt lugs and ensure they are machined properly. ive only seen it once, but i have seen a lug that was milled incorrectly and took more force to get the bolt to unlock and it slowed the carriers rearward motion enough to short stroke. Also even rarer, check to see if the carrier is loose in the upper and is "angling" downward at the rear of the carrier. this can cause the carrier to catch on the bottom of the buffer tube and again slow it down or lead to too much friction. This WILL leave marks on carrier/buffer tube at points of impact.
But most likely this is a simple fix...not enough "oomph" from gas system to drive your components backward to over power your spring. Just be careful you dont go too light on weight/tension of spring and buffer...as this can lead to the carrier coming too far back and contacting buffer tube.
Just an old Gunners mates advice.

 

[democracywins]

Are pistol buffer tubes generally the same size as that in a AR15 rifle? I know there are different sizes among fixed and adjustable stocks obviously. Just curious if I can try a few different springs to see if I can find something that works continually. I am guessing it is likely the spring and buffer. The upper I bought completed from JSE and Ive never had a problem with any of there uppers. However I will double check gas system just to make sure. Thanks for your help so far.

 

[avboiler11]

H or H2 buffer would likely fix the issue.

 

[tradertator]

AR's are inherently less reliable with a short barrel due to gas issues. Most people recommend at least an 11-1/2" barrel or running something like a suppressor or muzzle booster (like the Noveske KX3) which help create blowback, thus giving the gun more gas to work with. If your gas block is a bolt on though, the first thing I would check is if it is on in the correct location (not an issue with a pinned on one).