US Army fires off 3D printed RAMBO grenade launcher

Known as RAMBO (Rapid Additively Manufactured Ballistics Ordnance), the weapon was developed by the Army’s Armament Research, Development and Engineering Centre (ARDEC). RAMBO is based on the 40mm M203A1 grenade launcher, which contains 50 components. All of these, with the exception of springs and fasteners, were produced using various additive manufacturing techniques.

The barrel and receiver were fabricated from powdered aluminium using direct metal laser sintering (DMLS) in a process that took about 70 hours. After some machining and tumbling, they received Type III hard-coat anodising, just like a conventional M203A1. Other components, including the trigger and firing pin, were printed using 4340 alloy steel, which is the same material used to make the weapon by traditional methods.

Ammunition for RAMBO was developed by the Army’s Edgewood Chemical and Biological Centre (ECBC) and the Army Research Laboratory (ARL). They chose the M781 40mm training round, as it does not contain any explosives or propellants. The grenade’s windshield, projectile body and cartridge case were created using selective laser sintering and other processes. In order to try and replicate the rifling effect imparted on grenade rounds, the team had to experiment with various materials and techniques, as the zinc from which production M781 rounds are made cannot currently be 3D printed.