Caliber: 5.56 NATO/.223 Rem. ADCOR’s rifles use a ringless, gas-driven piston built into the top of the forward rail system. Adjustable cyclic rate, no carrier tilt, and a free-floating barrel. Forward ambi charging handle is non-reciprocating. Barrel lengths: 10.5, 14.5, 16 in. for 5.56. Rifle-length gas-system barrel lengths of 18 and 20 in. 1:7 twist chrome-lined barrels. Weight: 7 lbs.