Zenith Firearms ZF-300, Semi-automatic Rifle, 300 Blackout, 16 Threaded Barrel, Matte Finish, Black, Polymer, Free Float M-LOK Handguard, Collapsible Stock, Manual Safety, 30 Rounds, 3 Magazines ZF300BKOUT16 The ZF-300 16" is a semi-auto rifle with a roller-delayed blowback operating system. This pistol is chambered in 300BLK and comes with a full length Picatinny rail, & a cold hammer-forged barrel. The American Made ZF-300 also features a last round bolt hold open system. This firearm features a buffer tube compatible end cap, along with a buffer tube and stock.