AR jamming problem

[Jpach]

Buffer weight?

[Dragon]

it sounds like ammo . I had that same issue years ago when I used Ammo Bros ammo. It shot fine before i used theirs ,and it shot fine after i switched from theirs to another brand . Low powder rounds.

[RK808]

Alright, to answer all those questions, here we go:

The carbine upper was initially purchased complete from JSE Surplus. It initially had a low profile gas block. He was shooting Federal bulk pack .223, American Eagle .223, and eventually, tried American Eagle 5.56. It's not a magazine problem because we tried using plenty of magazines that work in other ARs including USGI, USGI w/ Magpul followers, and PMAGs.

We've put his upper onto my flawless lower and had the same problem so we eliminated the possibility of the buffer assembly being the problem. Back in its original configuration, we put my bolt carrier group and the problem persisted meaning that it's not the BCG. Even tried changing out the charging handle to see if there was gas leaking or some sort of abnormal contact on the bolt.

This was repeated when he bought a new A2 FSB, the same one that I'm running on my rifle with zero problems. Problems continued to exist so he got a new gas tube, and yes, it was carbine length.

I've built almost 10 ARs so I know it isn't a problem with mismatching parts or buying cheap, it has to be something like the gas port on the barrel or something like that.

[Pryde]

Open up the gas port.
It should measure .089 if its any smaller then that's your problem.
All you need is a drill press and its not that much work considering how much time you've put into it already.

Its also possible that its just a crap barrel with the gas port drilled off-center from where the gas block is pinned.

[Mail Clerk]

I'd check to see if your gas tube is dragging or hitting the gas key slightly. Insert the BCG and slowly see if the key drops over the gas tube without touching or causing any drag. Other than that my wild guess is you gas key is leaking.

Mail Clerk

[henmar77]

as mentioned i would check the gas block for blockage or mis-alignment.

[Flowmini98]

I've seen this happen with my cousins AR. A loose barrel and crappy American eagle ammo(black box) was the culprit

[homemade]

we run into this once in a while at the shop it could be a couple things
miss aligned gas port or gas port is not the correct size.
also one more issue we have run into a few times the barrel was modified and the gas port was too close to the end of the barrel and it didnt have enough gas to cycle the gun.
need at least 4 inches from end of the barrel to cycle reliably.

[USMCforLIFE]

i have seen this many times i bet its the mags heavily used mags do this often!

[hawaii five-0]

Does the "flawless lower"you put his jamming upper on have the same barrel length?Is it manufactured by the same company?If not,then it could be the buffer.Different barrel lengths/manufactureres require different buffers.

[ExtremeX]

Sounds like the gas port might be undersized...

Also try a higher power spring...

[hawaii five-0]

Another problem possibility is that the gas tube is slightly canted.This will cause the carrier to hang up.