What soldier has never dreamed of having RAMBO as a combat companion? This could soon be a reality thanks to U.S. Army researchers, whose 40mm RAMBO grenade launcher, made using additive manufacturing (commonly known as 3D printing), has just fired the first ammunition produced the same way. This is a world first, which confirms the relevance of the use of 3D printing technologies in a military context (as we wrote about here).
RAMBO (Rapid Additively Manufactured Ballistics Ordnance) is the result of six months of collaborative effort by the U.S. Army Research, Development and Engineering Command (RDECOM), the U.S. Army Manufacturing Technology (ManTech) Programme and America Makes, the national accelerator for additive manufacturing and 3-D printing.
The technology demonstrator did not aim to show that the grenade launcher and munition could be made cheaper, lighter or better than traditional mass-production methods but rather to determine whether AM technologies were mature enough to build an entire weapon system and the materials’ properties robust enough to create a properly functioning armament.
RAMBO is in fact a true copy of the famous M203A1 grenade launcher in service in the U.S. Armed Forces since 1969. Every component in the M203A1 grenade launcher, except springs and fasteners, was produced using AM techniques and processes. The barrel and receiver were fabricated in aluminium using a direct metal laser sintering process. Other components, like the trigger and firing pin, were printed in 4340 alloy steel, which matches the material of the traditional production parts. The process is certainly long, in the order of 70 hours to print and around five hours of post-process machining, and expensive, nearly €200 for a kilo of metal powder, but requires virtually no labour as the printers are automated, and the process leaves no scrap material behind.
Not content with having created a 3D weapon, ManTech also requested that a munition be printed. An integrated product team selected the M781 40mm training round because it is simple and does not involve any energetics: explosives, propellants and pyrotechnics are still awaiting approval for use in 3-D printing. But its zinc structure compelled the researchers to be imaginative, as 3D printing in zinc is not currently mastered by the U.S. Army. A great advantage of AM is that changes can be made quickly and there is no need for retooling, so four alternative approaches were taken to overcome this capability gap and produce the “40mm grenade of the future”.
RAMBO was then transferred to the 2-504 Parachute Infantry Regiment of the 82nd Airborne Division in order to refine the ergonomics of the system. As a result of feedback, U.S. Army engineers opted to create a stand-alone version of the M203 grenade launcher, usually attached to an assault rifle.
The printed grenade launcher and printed training rounds were live-fire tested for the first time on Oct. 12, 2016, at the Armament Technology Facility at Picatinny Arsenal, New Jersey and both performed as expected. For safety reasons the 15 test shots, performed outdoors and indoors, were fired remotely. RAMBO suffered no degradation during the tests but a slight design change was made to the munition following the appearance of cracks affecting the velocity of the ammunition.
The RAMBO system and associated components and rounds are undergoing further testing to evaluate reliability, survivability, failure rates and mechanisms.
Here you can read an article on this subject with many more technical explanations and details