"Rock River Arms AR1560 LAR-15 ATH Carb SA 223 Rem 18"" 30+1 Op Stk Black The LAR-15 ATH Carbine comes with a forged A4 upper receiver and a 18"" heavy match stainless barrel, air gauged and cryogenically treated with a 1:8 twist. Low Profile gas block. Trigger is two stage. Comes with ERGO sure grip. Star safety selector. The .223 Wylde chamber was designed as a match chambering for semi-automatic rifles. It will accommodate both .223 Rem and 5.56mm NATO ammunition. It is relieved in the case body to aid in extraction and features a shorter throat for improved accuracy."