I have an Adams Arms combined with a New Frontier polymer lower and LOVE it!
Quick question - did you install an extra-power hammer spring? If not, only about half of the surplus ammo will ignite. Also, with mine, I would get a random stoppage due to spent steel being deflected back into the chamber. Extractor was fine. Had me scratching my head. Went to an H2 buffer and all is well now.
5.45 is a wicked little round. There's an air pocket right behind the nose of the projectile and it does crazy stuff once it impacts. And it costs about half of .223. But some indoor ranges won't let you shoot any bullet that attracts a magnet like these will.