Army's Steadicam Third Arm – An Independent Study

Nicholas C
by Nicholas C

Recently an article has been circulating that the ARMY Research Lab is looking into a Steadicam third arm system to augment soldiers. Matthew Moss posted about it earlier this month. The idea is to help soldiers save energy by carrying the weight of their weapons. Before this article came out I already had plans to convert a Steadicam rig to hold a gun. Thanks to my friends, we were able to test my Steadicam third arm.

Steadicams x Guns = Awesome

For those who are not familiar with a Steadicam rig, it is a system that was developed in the 70s to support and stabilize film cameras used in Hollywood. It was put front and center in James Cameron’s Aliens. The Colonial Marines M56 Smartgun was a modified MG42 mounted onto a Steadicam third arm.

Image from Alien Anthology Wiki

This setup has been replicated by hardcore fans.

It works great for the movies but how well does it work for real firearms?

ARMY Research Labs Steadicam Third Arm

There was a photo almost 10 years ago of an HK G3 mounted to a Steadicam arm. However looking at the photo below they used the Steadicam as an alternative to a bipod.

Photo from "Steadicam Mounted Rifle" article here on TFB.

Here are some photos of the US ARMY Research Lab’s third arm.

Photo from

Their third arm is made of carbon fiber and weighs only 4 lbs. According to Armytimes, they have a newer prototype that weighs 3.5 lbs and can hold up to 20 lbs.

But Does It Work? Let’s Find Out

I had purchased a hobbyist Steadicam rig off Craigslist over a year ago. I had intended to mount a nerf gun or possibly airsoft just for fun. Yes, James Cameron’s Aliens influenced me a lot. While I was in Germany I had my friend Brian make a 3D printed articulated mount that would allow me to mount a rifle to the Steadicam arm.

Take a look at the video below.

In my haste to get a working prototype out I completely forgot an important aspect of this setup. Rolling the gun. I only planned for pitch and yaw. Being able to pan or tilt the gun up and down. Rolling the gun is very important, partially for aiming, but also checking the chamber and access to the weapon.

In the Army’s third arm, it is mounted to the top of the M4. This is a double-edged sword. By suspending the gun, it is better balanced. I tried both methods but height becomes an issue. It was easy to mount the gun on top of the arm mount and still be able to sight the gun while shooting. But the gun is not as steady. When mounted on top, the gun can easily flip upside down. When I attach the arm on top of the gun near the center of gravity, this is more naturally stable as the gun just hangs. But then the gun is physically lower and I cannot bring the gun up for a proper sight picture. This can be rectified with a new mount design. The Army third arm was designed to hold the gun from the top but this can interfere with optics on the gun. Also, not all guns have rails on top.

Take a look at the video below. I hang an HK 416 from the mount. You can see how it stays in position. If I mounted the HK 416 on top, then the gun would want to tilt upwards if I wasn’t holding onto it.

Another issue is since the Army has their arm positioned on the right-hand side of the shooter and the gun. The arm could interfere with ejection patterns of the rifles. I had the arm on my left side just like how it was in Aliens. I added an offset QD mount to the 3D printed mount so I could attach and detach the arm from guns quickly. One issue is that it would interfere with the belt box that hangs from the M249S. However, this could be easily rectified with a different QD mount.

I used a Midwest Industries MLOK handguard so I could attach the M249S to the Steadicam third arm. I also attached a Midevil Industries 360 VFG to the side similar to how the Aliens Smartgun has a horizontal grip for the support hand. It just needs a belt feeding backpack.

Thanks to The Range at Ballantyne for letting us use their indoor range.

But . . . But . . . You Can’t Go Prone

Image from Colonial Marines Technical Manual

This seems to be the number one ignorant complaint about a Steadicam third arm setup. While the Colonial Marines Technical Manual shows this drawing you see above. This method can work if you don’t care about having a sight picture. In the world of the Colonial Marines, the M56 Smart Gun has an infrared tracking system which feeds information into the HUD mounted on the Marine’s helmets. So unless you have something along the lines of Google Glass paired up to say a GoPro or a Tracking Point equipped rifle, you can’t aim properly.

The Steadicam setup is like a sling. It helps shift the weight of the firearm to your upper torso. If the sling prevents you from going prone, you just get out of the sling or detach the gun from the sling. The same process applies to the Steadicam third arm. As I said earlier, my setup was modified with a QD mount so I can quickly remove the gun from the arm. I can swing the arm out of the way and go prone. Or just remove the arm entirely from my vest in a couple of seconds and then go prone.

The range of motion is not really affected. Bending over is slightly compromised but I was able to kneel down and sit on the ground with this Steadicam third arm setup. Because of the range of motion of the arm, I would have to lean my torso to raise the aim of the gun up or down respectively.

Another issue is the idea of “weight savings”. You aren’t really saving weight since you are adding more weight to a soldier’s loadout. However like proper backpacking technique you want your load on the hips. If the Army designs their third arm properly, it would apply the weight of the gun to the hips. Having briefly manipulated the M249S and a full auto M249 on my Steadicam third arm, I can say that it works. The FN M249S weighs 17.2 lbs and although it overwhelmed the Steadicam arms, it did help take some of the weight off my arms. Alex’s full auto M249 was lighter and 90% of the gun was held up by the third arm and made shooting the M249 effortless.

The Steadicam third arm is basically a mobile shooting platform somewhat like shooting sticks that is mounted to your torso. It just holds up the gun. It does not affect recoil since there is little to no resistance in the arm. It is simple physics. X vs Y axis. The weight of the gun is along the y-axis and supported by the third arm. Recoil is on the X-axis and the only thing stopping it is your body.

Unintended Benefit

The most surprising yet positive feedback I have received about my Steadicam third arm tests was how it could apply to disabled people. Specifically amputees. Sure there are stabilizing braces for large pistols like the AR-15 pistol, but manipulating a long gun with only one arm is challenging. There are some issues that would need to be addressed. Like mounting and dismounting the gun to the Steadicam would be difficult with just one arm. Manipulation like one-handed mag changes would be difficult as well while the gun is mounted. However, I am sure with practice these issues could be easily addressed. You could even attach a crossbow to this setup and hunt one-handed. One way to make the Steadicam more hunting friendly would be to possibly attach a hog saddle. Then any rifle could be attached and supported by the Steadicam arm.

Brian Miller experimenting with his PTR91 and seeing how feasible the steadicam rig is for one handed operation.

Shooting a Vepr12 one handed.

Almost There

There are some issues that need to be addressed. When and where to use this. I have never been in the army so I don’t know what soldiers, specifically those who carry belt feds, have to go through. Do they spend a lot of time on patrol walking with their M249 or M240? If so then I could see the merit of the Steadicam third arm. How often do they run and gun with said belt feds? Would this help take the weight off their arms? I think so. The springs do need to be changed out to hold up more weight for heavier guns. One idea would be to make this third arm mount to vehicles for stabilized shooting while the vehicle is moving.

Nicholas C
Nicholas C

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  • TGM TGM on Apr 06, 2018

    The most promising application of a 3rd arm system would be making heavier weapons (25lb+ LMGs) more useful for shooting on the move. It is very premature to mock these early experiments.

  • Blue Centurion Blue Centurion on Apr 08, 2018

    This will work perfectly for the female infantry, as well as a mount for a soldier's Flat Screen TV when gaming in the field!