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.