This is a Short Barreled Rifle (SBR) version of the UDP-9. ALL NFA RULES APPLY. The UDP-9 with Magpul CTR stock is a compact AR-15 style firearm chambered in 9mm. It features last round bolt hold open. Technical Specifications Last round bolt hold open on an empty magazine Flared magwell for faster reloads Integrated, oversized trigger guard 7075-T6 billet aluminum lower with a matte black hard-coat anodized finish 7075-T6 billet aluminum slick side upper receiver with appropriately sized ejection port and no forward assist or dust cover Threaded bolt catch screw 9mm bolt assembly for use with a standard AR-15 hammer 6" 9mm barrel in chrome moly with a 1/10 twist, black melonite finish and A2 style flash suppressor Barrel is threaded 1/2x36 and can accept a suppressor Magpul CTR Buttstock Magpul K2 pistol grip Angstadt Arms 5.5" free float M-LOK hand guard with a modern, ergonomic, 7 side design that allows for 45 degree offset mounting options Continuous top mil-spec 1913 picatinny rail Patent pending Accepts all Glock(R) aftermarket magazines. We recommend using factory Glock(R) magazines Includes one 15 round magazine