3D printed weapons are nothing new. Plenty of people have tried 3D printing guns and other weapons in the past. Researchers at the U.S. Army Armament Research, Development and Engineering Center (ARDEC) have not only 3D printed a grenade but also launched it using a 3D printed grenade launcher.
RAMBO (Rapid Additively Manufactured Ballistics Ordnance) has 50+ components, all of which except for springs and fasteners were produced with 3D printing. The barrel and receiver were made in aluminum using a DMLS process in about 70 hours. The above video shows this grenade launcher in action.