Meet RAMBO, the U.S. Army's 3D-Printed Grenade Launcher

Meet RAMBO, the U.S. Army's 3D-Printed Grenade Launcher

The U.S. Army has built and fired an almost entirely 3D-printed 40mm grenade launcher. Scientists and engineers hope the prototype will set the stage for projects in the laboratory and on the battlefield.

The Armament Research, Development and Engineering Center (ARDEC) at Picatinny Arsenal in New Jersey modeled the proof-of-concept Rapid Additively Manufactured Ballistics Ordnance (RAMBO) on the Army-standard M203 grenade launcher and marked it “M203XX.” The production process for 90 percent of the components was at least partially automated, though engineers had to assemble the final weapons by hand. Certain springs and fasteners were too small and complex for a 3D printer. The project also produced training rounds based on the M781, but engineers had to manually add the explosive propellant right before the test shots.

A number of other Army research and development and engineering activities, as well as other laboratories across the U.S. military and private companies, contributed to the project. These partners included the Army Manufacturing Program (ManTech), the Army Research Laboratory (ARL), the Edgewood Chemical Biological Center (ECBC), and the Natick Soldier Research, Development and Engineering Center (NSRDEC).

“We chose the 40mm because it's a relatively simple system, with the pressure and speeds involved,” Sunny Burns, an ARDEC materials engineer, explained to the service’s reporters. “It's low velocity and low pressure so it's not as critical as a small caliber system.”

So, while the printers involved could have built a close approximation of almost any weapon, the materials available not have been strong enough to withstand the shock of even experimental use. First developed in 1950s, the Army’s low-velocity 40mm cartridges already have a particular design to keep pressure and felt recoil low, but still lob relatively large projectiles hundreds of feet away.

The RAMBO barrel assembly (top) and a standard one from an M203A1 for comparison.

RAMBO is far from flimsy. Though many people think of 3D printing – or as the U.S. military prefers “additive manufacturing” – as only involving plastics, industrial printers can craft parts from a variety of materials. Picatinny’s grenade launcher features plastic and resin pieces, as well as aluminum and steel components. 

"We've tried to stay as much one-to-one as possible," Burns said. “So if a part was aluminum we didn't want to print in steel, we wanted to print in aluminum.”

Beyond the varied materials, RAMBO is a testament to how far 3D-printing technology has improved over the years. ARDEC’s printers can make up complicated shapes that might have been an impossible proposition not too long ago. Most notably, the launcher’s barrel had to be rifled. The Army’s M203s and newer M320s both spin the 40mm grenades both for accuracy and safety. The rotating movement arms the rounds after they’ve traveled a certain distance, preventing them from blowing up in the shooter’s face.

Rifling is “a pretty tricky process to get the tooling, and things like that take a lot of experience,” Burns noted. “Only one machinist in our machine shop had any experience doing it and we have around 30 machinists here.”

ARDEC estimated it would’ve cost $50,000 to buy the equipment necessary to make a rifled 40mm barrel through the traditional method. This would have been prohibitively expensive for just one RAMBO prototype, even if technicians made a small batch of 10 to 12 for the project.

However, the experiment wasn't without problems. ARDEC’s machinery couldn’t build up all of the parts of the training round using the normal materials. The mass-produced M781s have a reinforced nylon cartridge case. The staff at Picatinny couldn’t print in that particular polymer, so they used other glass-filled plastics. Unfortunately, these substitutes weren’t strong enough and cracked during testing, which could have been potentially dangerous. Engineers ultimately redesigned the round to toughen up certain areas.


A mix of 3D-printed training grenade and production M781 components.

But this is exactly what the Army and its sister services hope to get out of 3D printing. Rapid prototyping can speed up development of new systems, simplify the process of making changes, and generally reduce costs. Instead of having to buy tens of thousands of dollars of specialized equipment and paying specially trained contractors, engineers can draw a component on a computer and print it out with relative ease. Picatinny turned out most of the parts for RAMBO in less than 48 hours.

If something goes wrong, all that you need to do is go back into the computer model, refine the design, and repeat the process. During the RAMBO project, this is exactly what happened with case design for the training grenades. ARDEC is also exploring whether or not the additive manufacturing process can ultimately include 3D-printed explosive charges for future prototype ammunition.

In addition, the Army is looking to see if these methods are useful outside a laboratory or test workshop setting. One of ARDEC's ideas is to give troops in the field the ability to quickly make up new weapon accessories and components. RAMBO has a 3D-printed rear pistol grip and rail attachment points. In the future, if soldiers didn’t like the grip angle or needed more space for sights, lasers, or other systems, they might be able to have a unit armorer just print out different options.

“Some soldiers like a 45 degree grip handle in the front on their rifle and some like a 90 degree grip handle in the front,” Jim Zunino, another materials engineer at ARDEC, said. “With additive manufacturing we could potentially customize to each soldier's liking.”


A U.S. Air Force airman fires an M203 grenade launcher attached to an M4 carbine.

To this end, Picatinny is working on a concept involving forward-deployed teams with “expeditionary kits” of 3D printers and materials who can quickly fabricate new parts in the field. They might not even need to make entirely new components. If someone doesn’t like they handling of their weapon, engineers might simply be able to draw up pieces that fit onto the existing features without time-consuming modifications.

The basic principle ARDEC is describing already exists on the private market in the United States. Magpul, which makes firearms and accessories, has what it calls a Mission Adaptable (MAID) pistol grip for AR-15- and M16-pattern weapons. With the arrangement, a shooter can easily replace the back strap and adjust the overall contour to their liking. Other companies make similar products for the AR-15/M16 family and other guns. In fact, a large portion of the polymer pistol market now has interchangeable grip panels and back-straps. With the right materials, the Army could simply 3D print these optional pieces.

This plan would build on the experience of the Army’s Rapid Equipping Force, as well. Since 2004, the REF has sent teams of engineers and technicians to Iraq and Afghanistan to help quickly produce prototype systems and solve urgent requirements. The unit began fielding “Expeditionary Labs” (ExLabs), which were 20-foot shipping containers kitted out as transportable workshops. As of 2014, the group had two 3D printers in its ExLabs Afghanistan.

"You're not going to be able to make a grenade launcher in one of the expeditionary kits we're building, but if you want an additional Picatinny rail or grip we want to be able to give them that ability," Zunino made clear.


Experimental cased-telescoped ammunition, with polymer cases (top), and caseless ammunition.

On top of that, it’s possible ARDEC’s research could lead to improvements in the manufacturing of polymer-cased ammunition. Since the early 2000s, the Army has been actively working on a succession of small programs exploring the potential of caseless, cased-telescoped and polymer-cased ammunition. The main goal of all these concepts is to reduce the amount of weight an individual soldier has to carry.

For more than a century now, companies have almost universally built small arms rounds with metal cartridge cases. With troops carrying hundreds of rounds, that weight quickly adds up. It’s not cheap, either. Using cases made of high-strength plastics or getting rid of them altogether, along with lighter magazines, would ease the burden on many soldiers in the field. Others services are interested in the concept too.

“We have to have lighter equipment,” William Williford, executive director of Marine Corp Systems Command, said at the Navy League’s Sea, Air, Space 2017 conventional and exposition. Williford specifically mentioned polymer cartridges and magazines, but added that just transporting ammunition cans on plastic pallets might be a good place to start.

In partnership with the Marines, other Army units, or elements elsewhere within the U.S. military, ARDEC could conceivably help fabricate prototypes of any of these systems of its 3D printers. And in a future combat situation, its engineers might be able to build up replacements on the spot.

“We're trying to explore what other techniques are out there that could be complimentary to current and future weapon system production,” Zunino said.