New PDI Patriot Kit available at Redwolf Airsoft... "Convert your Tokyo Marui M4A1, M733, SR16 or M16A2 into a Patriot system with shortened barrel, battery stored internally in rear shaft type stock. Full metal construction for an ultra-compact SMG that's very tactical looking. Full instructions included and user installable. Inner Barrel is 141mm long, and has a 8.9mm diameter. 

he whole gear will be 490mm after modification. All parts are made of duralmin, and are high-quality machined-metal. Battery is fitted in the rear. When attaching it to an M4A1 or M733, a little re-wiring is needed due to the placement of the battery. This set includes: Outer barrel / Hand gurd / Front cap / Rear ring / Battery case / Battery case joint / swivel pin /gus block / muzzle. The body, mag, battery & Sight are not included."