Fixing an AR15 upper

[rvicta]

The barrel is, according to the tag:

"20" 1:7 Cold Hammer Forged Spiral Flute
Adjustable Gas Key
Rifle-length Gas System
Nitride MPI BCG
15" Keymod Rail
Nitride Low-pro Gas Block
Ambi-Charging Handle
Linear Compensator"

I was using American Eagle 75 grain FMJ. There isn't really anything else on the shelves here, so I hadn't tested other factory ammo.

The fired brass has scratches on the body of the case towards the head; it's unscratched from the neck to about the middle. I don't have a web location yet to post photos.

It was brand new when I tested it. I cleaned it at the range to try to fix, but I can do a more thorough job. Though, I don't think I want the rifle to be so finicky about dirt for proper extraction.

I'm in Northern CA.

I saw you mentioned an adjustable gas key. Try adjustments to that to see if it helps.

[God Bless America]

Are you using a 5.56 bolt on your .224 barrel? The bolt needs to be for a 6.8 SPC. Check and see if you have the proper bolt for the barrel extension.

It chambered and fired, then stuck.

[ozarkpugs@gmail.com]

It is not an undergassed problem if the case is stuck in the chamber and has to be banged out .You can turn the block around and block the flow completely and just use the charging handle to eject with no banging . Have you really - really cleaned the chamber ? How does the spent cartridge look?

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[el tardo]

To OP
This will help lead you in the right direction-

First thing is take the upper off the lower, put a round in the chamber and make sure the bolt carrier group will extract it.
Again we’re guessing but this will give you a better idea of the boat carrier group is operating correctly.

I’m not concerned if the gas system is operating or not we’re trying to find out if you have other problems first.

This step you need to be at a range unfortunately -
With the magazine out at the range with the upper on the lower load one round and fire it. Again just like above can you pull the charging handle to manually extract the round? What happens at this point? If you cannot manually pull the charging handle the problem you’re having is not the gas system and something else.
Now if you can pull the charging handle and it pulls the round out the boat carrier group is operating like it supposed to then the next step is adjusting the gas block. But I don’t even think you’re there and the problem is you’re saying you’re having.

The nice guy that is probably the best gunsmith I’ve ever met that is also posting here is a Randell ( ar15barrels) And I would recommend you ship your upper to him to have it fixed. No he’s not in Norcal he’s in SoCal but I could say I’ve been using him for five years and the guy knows his stuff

[God Bless America]

Or should I try something else first?

Thanks for any advice.

Can you manually run a mag of ammo through the gun without firing, so that the BCG closes all the way each time?

Post pics of fired brass, as requested above. You might have a chamber problem.

[ar15barrels]

Can you manually run a mag of ammo through the gun without firing, so that the BCG closes all the way each time?

Manually cycling ammo through a rifle action only tellls is about headspace and it only tells us if the ammo is long or the chamber is short, but it does not tell us if either are actually in spec.
It also won’t tell us anything about feeding, cycling or extracting/ejecting as doing any of those manually is nothing like the actual conditions of live fire.

We see this year after year where someone posts a thread that their rifle won’t properly feed or extract or cycle or function and then the truth comes out that they are only testing with dummie cartridges or hand cycling live ammo.

The solution is always to oil up the gun and run 100 rounds through it and then see if there is actually a problem.

[God Bless America]

He can manually cycle in the comfort of his own home, without a trip to the range.

He explained that it locks up upon firing, which could be a chambering issue. He did not complain about feeding etc.
He tried to fire several dozen at the range but it repeatedly locked up.

If he has trouble chambering rounds, then an improperly-chambered upper is again suspect.

It costs nothing but a few minutes and tells us possibly something. Maybe nothing.

A fired case, as requested above, would be more telling, but he has not posted pics. Maybe he left them at the range.

[SDnewbieshooter]

It sounds like something that happened to a upper I got: Fired one shot, bolt is jammed, couldn't pull the bolt back without banging on the stock a couple times.

In my case, the problem was under-gassing. They installed a carbine length gas tube in a mid-length system. After replacing the gas tube the problem went away.

It's possible that the same applies here: Not enough gas to the bolt fully cycle it, but just enough to get it stuck with a spent casing.

[ozarkpugs@gmail.com]

How in heck does someone install a tube that is 2" too short. If you leave the tube off it will not cause the empty cartridge to lock up it will just be a repeater that has to have the charge handle pulled every shot . I bet if he gets the chamber cleaned and maybe polished and cleans and lubed the carrier it will run unless the chamber is just a hacked up job

It sounds like something that happened to a upper I got: Fired one shot, bolt is jammed, couldn't pull the bolt back without banging on the stock a couple times.

In my case, the problem was under-gassing. They installed a carbine length gas tube in a mid-length system. After replacing the gas tube the problem went away.

It's possible that the same applies here: Not enough gas to the bolt fully cycle it, but just enough to get it stuck with a spent casing.

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