Im on my 4th black rifle but sold one a few years ago and wish i hadnt.
Rock River CAR4 5.56 flat top
S&W MP-15/22LR
DPMS Oracle 5.56
Colt M16 .22LR
Having to send the MP15 back to S&W because of the extractor "disappearing" somehow (still havent figured that one out) and about 3" from the muzzle inside the barrel there is a groove that runs around the entire bore, not sure whats up there.