Need help with 10.5" Pistol trouble shooting

[amac]

I gave my son a pistol build kit for Christmas. He assembled a Spikes Tactical enhanced lower kit and added an SBA3 brace. For the upper, I gave him my 10.5% Noveske upper that has been running flawless on my SBR Noveske lower. I've put numerous rounds suppressed and unsuppressed through the upper on my lower. My son took his new Pistol AR to the range today and experienced some failures to feed, failures to lock back on empty and a few times, the trigger wouldn't reset. He didn't keep exact count of failures to successful cycles, but my discussion with him leads me to think maybe 10-15 (maybe a few more) failures out of 200 rounds shot. Not a bad percentage, but not 100% reliable like my SBR.

I don't think it's a gas port issue because the upper reliably cycles on my lower. I'm shelving this topic until I've exhausted everything else.

I measured both buffer tubes and they are the same. I gave him the same buffer spring and H2 weight that I was using. He did switch out to a standard buffer weight and experienced similar issues. He said more trigger related with the standard buffer weight than feeding or lock backs.

He was shooting a "bucket" of Remington UMC 223 ammo purchased from Cabella's. This is my primary guess for "gassing" issues. Maybe this ammo is weak? I will go with him on the next outing and bring various ammo I have on hand. Mostly PMC brass.

Before next outing, I will clean and inspect the bolt and gas rings. I will make sure to heavily lube everything before shooting.

Outside of the above I've mentioned, what other aspects of the failures am I missing and should inspect?

Thanks for the feedback.

[amac]

More thoughts on my cycling issue... ammo is at the top of my list. I was just reading up on buffer springs and weights and read that a bolt could cycle too fast and not pick up the next round. That sounds like what my son was describing and if so, a heavier buffer would be needed. Then, why or what causes a trigger to not reset after firing a round? I manually cycled the weapon and the trigger clicked every time.

My assumption is the bolt isn’t traveling far enough back to pick up a round and reset the trigger. Anyone else experience this and found a solution?

[jesuvuah]

Did he install the trigger disconnector 9r perhaps the spring for it?

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[markm]

UMC is garbage, and I'd second the idea that some error was made in the LPK installation for reset issues to be happening... that or out of spec components in the LPK.

[amac]

Did he install the trigger disconnector 9r perhaps the spring for it?

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Not sure what 9r means? You suggesting a backwards installation? If that were the case, would the trigger function at all? He fired 190 or so successful times. I wouldn’t think out of spec or bad instal to be the culprit. However, it’s easy enough to pull the trigger and reinstall.

Any thoughts on the spring or buffer?

[Diamondback]

Not sure what 9r means? You suggesting a backwards installation? If that were the case, would the trigger function at all? He fired 190 or so successful times. I wouldn’t think out of spec or bad instal to be the culprit. However, it’s easy enough to pull the trigger and reinstall.

Any thoughts on the spring or buffer?

Looks like a typo, probably meant "disconnector OR spring" given that 9 is right above O on most keyboards.

[MistWolf]

First things first. Get in spec ammo and perform a lock back check- that is, place a single round in a mag known to properly function, load your AR and fire it. Check to see if the bolt locks back. Do this a few times for verification.

[themonk]

First things first. Get in spec ammo and perform a lock back check- that is, place a single round in a mag known to properly function, load your AR and fire it. Check to see if the bolt locks back. Do this a few times for verification.

Mist, why would you do ammo testing first. Seems like pulling the trigger and doing a proper install can be done at home in 10 min.