I have one. Has 1,786 Documented rounds through it, from Mk262 Mod 0/1 to .223 PMC Bronze... Runs Flawlessly. Zero Malfs or Issues... Locks back on empty mags. Runs on A5H1 & A5H2 Buffers with Green Sprinco. Very Soft & Smooth.

https://www.m4carbine.net/showthread...-5-shot-Groups

https://www.m4carbine.net/showthread...ipped-MK/page8

https://www.m4carbine.net/showthread...ook-like/page4