Caliber: 5.56 NATO. Barrels: 11.5”, 13.7”, 14.5”, 16”, free-floated, hammer-forged, 1:7 twist, chrome-lined. Mil-spec proprietary mid-length self-indexing gas system with straight gas tube design. Gas block held in place with a nut, simplifying removal and maintenance. E3.2 enhanced bolt has an enlarged bolt face, dual ejectors, rounded bolt lugs, reduced diameter cam pin, and proprietary extractor and firing-pin designs. Improves ejection performance with suppressors on short-barreled carbines. Other updates in Mod 2.6 include proprietary free-floating URX 6 handguard, mirrored bolt catch and release, ambidextrous magazine release, selector, and charging handle. Quick Detach Coupling (QDC) flash hiders, drop-in two-stage match trigger. Models: KS-1 (13.7” heavy-profile barrel with ball-mill dimpling mid-length gas system, 6.88 lbs., 30.3” to 33.5” long.); KS-2 (14.5” light-profile barrel with mid-length gas system, 6.44 lbs., 31” to 34.3” long); KS-3 (11.5” barrel, 6.1 lbs., 28” to 31.3” long); KS-4 (16” barrel with extended mid-length gas system that utilizes a 15” variant of the URX handguard, 6.62 lbs., 32.5” to 35.75” long).