This is a  DPMS lower, Bushmaster (purple) 14.5 with AK brake and M&A upper. The telescopic sight is a Trijicon model TA50-4 compact ACOG. See my ACOG web page for details on this fine sight. This upper started life on top of my Hesse lower receiver but I gave up on getting the lower to function correctly. See my Hesse page to view some of its issues.

Dpms with ACOG
DPMS Carbine Close Up
DPMS Carbine