Caliber: 5.56 NATO. Rifle Downward-ejection Bullpup, but otherwise similar in configuration to RFB. 20-round magazine, accepts AR-15 magazines. Barrel: 17.3” 1:7 twist with threaded muzzle, A2-style flash hider. Black finish. Weight: 7 lbs. Length: 27.3”. Defender has an aluminum M-LOK handguard, collapsible stock, and 16” pencil-profile barrel. Hunter has a hunter-style grip and modified handguard. Survival has a hunter grip, 16” barrel, folding iron sights. Introduced 2015. Values are for the RDB17; add 9.4% for the RBD Hunter and RBD Survival models; add 19% for the RBD Defender variant.