Checking to see if you guys do any "tuning" of firearms. I have an upper that operates as if it's under-gassed (won't hold back bolt on last round; won't feed rounds after first shot). I believe it may be because it wasn't assembled properly (you guys did NOT do this build).

It's a Colt A2 upper with a Colt M4CQB 10.3" barrel.

https://www.ar15.com/forums/armory/Need-Help-with-SBR-Build-Non-Functional/51-549961/

We can take a look at the upper, but we're swamped right now doing standard thread jobs, so it may sit for a few weeks.