Caliber: 5.56 NATO, 300 BLK. Barrel: 16”, 1:8 twist. S.D. is suppressor-ready rifle with ambidextrous controls, adjustable gas block, chrome-lined 416 stainless-steel cold hammer-forged barrel. Direct-impingement operating system. Geissele Super Dynamic-Combat (SD-C) nonadjustable two-state trigger. Proprietary 13.7” handguard has four stainless-steel anti-rotation QD points. Magpul MBUS 3 sights. 14.5” barrel has pinned-and-welded Dead Air KeyMo three-prong flash hider for 16” overall barrel length. Black, OD Green, or FDE finishes. 30-round magazine. Standard rifle has ALG Defense Advanced Combat Trigger, A2 flash hider, non-ambi controls. Lifetime warranty. In May 2023, Watchtower Firearms acquired F-1 Firearms. Made in Spring, Texas. Introduced 2026. Values are for the Standard Issue variant; add 46% for the Special Duty variant.