First AR lots of malfunctions.

[Iraqgunz]

Well since you took it apart. Is that barrel dimpled below the gas block? Why do you expect sending it back again is going to change the outcome?

*update*

Ok, folks. It’s been a while, mainly because I got tired of dealing with it, and set it aside.

In short, nothing got fixed.

What happened was, while I was waiting for a update from PSA (I had called then a couple times and they said the backlog had been extended because of their lifetime warranty.) I got the notice that it was waiting for me at UPS. Great!

So I picked it up and it looked like nothing had been done to it. I hadn’t sent it out clean so I wasn’t sure. Well, I called them up to ask what they had fixed, and they said “Nothing. We ran 3 mags through it with no problems.” WTF? But if I still had trouble, I “could send it back again.” So I asked what mags they used. “P-mags” they said. So I went out, bought a gen 2 P-mag, went shooting, and had the exact same problems as before. Couldn’t get through a single mag without malfunctions, from any of the 3 ammos I was using.

This time I took apart the gas block and tube, checked for obstructions, alignment, and proper port size. All check out ok.

I’m going to sent it back again and go from there. I don't have anywhere to shoot rifle in the winter anyway.

[Outlander Systems]

Unless something has changed recently, PSA does not dimple their barrels for their low-profile gas blocks.

Well since you took it apart. Is that barrel dimpled below the gas block? Why do you expect sending it back again is going to change the outcome?

[Iraqgunz]

Which is exactly why I asked.

Unless something has changed recently, PSA does not dimple their barrels for their low-profile gas blocks.

[Hammer_Man]

Op what ammo are you using? Are you using quality factory ammo (Federal XM193, XM855, etc..) or are you using reloads?

[georgeib]

Op what ammo are you using? Are you using quality factory ammo (Federal XM193, XM855, etc..) or are you using reloads?

Look at the original post...

[Hmac]

Op what ammo are you using? Are you using quality factory ammo (Federal XM193, XM855, etc..) or are you using reloads?

IMHO, that shouldn't matter. A minimally functional AR15 should run fine independent of ammo. If you can't go to the gun store and buy basic garden-variety 5.56 or .223 ammo off the shelf and have it run just fine in your rifle than you have a lemon.

[Hammer_Man]

IMHO, that shouldn't matter. A minimally functional AR15 should run fine independent of ammo. If you can't go to the gun store and buy basic garden-variety 5.56 or .223 ammo off the shelf and have it run just fine in your rifle than you have a lemon.

I only asked because I've fired reloads through my pistol that were too weak to cycle the action properly. In essence my P226 was short stroking due to an inadequate powder charge in the cartridges I bought. I figured an AR15 would not behave differently if it were fed substandard ammunition.

[Stickman]

I only asked because I've fired reloads through my pistol that were too weak to cycle the action properly. In essence my P226 was short stroking due to an inadequate powder charge in the cartridges I bought. I figured an AR15 would not behave differently if it were fed substandard ammunition.

Correct, but PSA and others hog out the gas port so that shouldn’t be an issue even with weak ammo.

[crosseyedshooter]

When I had occasional failure to cycle on a new rifle, I had to methodically check each part of the operating cycle. There have been some great suggestions for a lock back test already. To solve my issue, I identified all of the symptoms, then I diagnosed each one. The main symptom that stands out from the OP is failure to lock back.

Mistwolf already provided excellent advice about a lock back test in post 14. Perform the test with known good factory ammo and proven magazine. The AR15 is a straightforward mechanical device, failure to lock back is typically due to short stroking, weak magazine spring, some variation of out of spec bolt-catch and lastly excessive bolt velocity outrunning the previous parts. Thing is, short stroking and excess bolt velocity are nearly opposite problems so you need to clearly identify your problem.

If you’re already convinced it’s short-stroking, the AR15 is gas operated, so just check from the buffer system all the way to the gas system, back to front. What’s even more convenient is that the two systems are separated into upper and lower receivers! If anyone near you has a working AR, you can swap uppers/lowers to isolate the problem. If it’s a spring/buffer issue, it’ll follow the lower. If it’s a gas system issue it’ll follow the upper.

To troubleshoot yourself without known good parts is a bit of a challenge; make sure the spring and buffer aren’t too heavy/stiff and you have full travel of the bolt going back. Manually pulling the charging handle you should smoothly bottom out with the bolt face about 1/4” behind the bolt catch. Make sure the buffer is applying force to the rear of the bolt when rifle is assembled. Assuming buffer/spring system is in spec with unimpeded travel, move on to the gas system in upper.

Check that the bolt slides smoothly in the upper and the gas key is aligned to the gas tube. Check that the gas tube has a slight flare to help mate with the gas key. Take out the bolt carrier group and check the gas rings. On a new bolt/rifle, all of my bolts will remain extended under the weight of the carrier. Check the gas key for looseness, proper staking. Check cam pin and path for gouging/burrs. Take out the bolt and inspect the gas rings and carrier ID for scoring, burrs, defects along the cylinder wall. Assuming bolt carrier group is good, continue moving forward.

Check for obvious leaks in the gas system such as carbon blowing out at the gas tube/block junctions. Make sure the gas block is aligned vertically at 12 o’clock and axially along the barrel. Depending on the barrel profile, there’s typically a small gap between back of gas block and shoulder of the barrel about the thickness of an M4 handguard ring. If still nothing obvious, disassemble the gas block and look at the carbon rings to show gas port alignment. Then measure the gas port while you’re in there.

Here’s the short version instead of inspecting everything:
1. Swap upper and lower with known good rifle and perform lock back test.
2. Swap bolt carrier group with known good part and perform lock back test.

[crosseyedshooter]

*update*
This time I took apart the gas block and tube, checked for obstructions, alignment, and proper port size. All check out ok.

Did you measure the gas port diameter with pin gauges and what was the result?