Mil. Spec. Forged 7075-T6 Aluminum YHM Flat Top Upper Receiver "T" Marked Upper Receiver Forward Assist Installed CMMG Ramped 9mm Bolt Carrier Assembly (YHM-921-BA) 16" Chrome-Moly Vanadium Steel Barrel, Heat Treated to RC 25-32, Threaded 1/2"-36 Chambered in 9X19mm, with a 1:14", 6 groove Twist YHM 9mm Phantom 5C2 Flash Hider/Compensator (YHM-80-5C2) YHM Carbine Length Handguard (YHM-9645) YHM Single Rail Gas Block (YHM-9385-A)
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Fantastic upper. Fits nicely on my CMMG lower (why shouldn't it), and the ramped bolt means a special 9mm-compatible hammer isn't required. I happen to have a HiperFire 24C trigger which works without issue.
So far I've only tried 115gr ammo, Blazer Brass and TulAmmo steel case. No failures to fire, but the steel case has failed to fully cycle a few times, either not resetting the hammer and once catching an ejected case. Lesson learned - just use brass.
Happily making big ragged-edged holes with just a basic red dot sight.