Weapons of Note: The Gyrojet Rocket Rifle

By: Friedrich Seiltgen

Copyright © 2024

THE DEVELOPMENT

The Gyrojet concept was a line of firearms using gyroscopically stabilized projectiles ranging in caliber from 6mm to 20mm. There was a rifle, carbine, and a pistol version.

In 1960, Robert Mainhardt and Art Biehl formed MB Associates (MBA) to develop a small arms projectile using solid rocket fuel as a propellant instead of gunpowder.

Unlike conventional munitions, which use a grooved barrel to spin the round for accuracy, the Gyrojet rounds were basically tiny rockets filled with solid propellant. They featured four angled ports at the rear of the case, causing them to spin at 19,000 revolutions per minute and stabilize. When fired, the propellant burned for approximately 1/10 of a second, giving the projectile a velocity of 1,500 feet per second. The combustion gases released from the projectile were pushed out of the barrel using vent holes.

Conventional firearms create pressure in the barrel, with maximum energy at the muzzle, and require a substantial barrel to handle the pressure. Since the microjet picked up speed until the propellant ran out, the pressure was low, so the barrel was essentially a standard tube.

THE PISTOL

The Gyrojet Pistol, aka the “Rocketeer,” fired a 13mm microjet. It featured an integral magazine, so the microjet had to be loaded from the top. To fire the weapon, a lever above the trigger was pushed forward to chamber a microjet. When the trigger was pulled, the lever struck the microjet nose, forcing the round into the firing pin. When the pressure was high enough, the microjet would override the lever’s force and push it back down. Needless to say, reloads were not fast.

The pistol required a few changes due to the U.S. government. The Gun Control Act of 1968 classified the Gyrojet as a destructive device as it had an explosive-filled projectile over a half-inch in diameter. This required a tax stamp and paperwork. MBA created the Gyrojet Mark II to get around the new law, which fired a 12mm/180-grain rocket.

OPERATING SYSTEM

When the trigger is depressed, the hammer in front of the round strikes the projectile, pushing it into the firing pin and igniting the projectile. The hammer briefly holds the round in place to allow it to gain energy and then moves out of the way, allowing the round to travel down range.

THE ROCKETS

Designer Robert Mainhardt called in his friend Nick Minchakievich to help with the stabilization issues of the rockets, or microjets as they were called. The original microjets used rear ignition, which proved dangerous in a shoulder-fired weapon. Minchakievich believed that retractable fins were the way to go, but they required advanced machining and were too expensive to produce. Minchakievich then used diagonal vented ports to make the projectiles spin and stabilize them gyroscopically like a rifle. Another issue was the ports allowed moisture into the microjets, which created a reliability problem with the fuel.

Minchakievich continued working on the projectile design and requested more time to perfect an accurate projectile, but time was running out. He even tried to get the help of “Star Trek” Producer Gene Roddenberry to use the pistol in a “Star Trek” episode to no avail. The Gyrojet rifle and pistol did make it to the big screen in the James Bond film “You Only Live Twice” and the Matt Helm film “Murderers’ Row.”

In the end, the Gyrojet was a failure. It was inaccurate and unreliable, and the day’s technology could not save the concept. As the Vietnam War raged on, other options were already in production, and the project’s high cost sealed its fate.

Today, the remaining Gyrojet models in circulation are coveted collector’s items that bring high prices.

That’s all for now, folks! Please keep sending in your questions, tips, and article ideas. And as always – “Let’s Be Careful Out There.”

Friedrich Seiltgen is a retired Master Police Officer with 20 years of service with the Orlando Police Department. His writing has appeared in The Armory Life, RECOIL, Floridajolt.com, Soldier of Fortune, Off Grid, The Counter Terrorist Magazine, American Thinker, Homeland Security Today, and The Journal of Counterterrorism & Homeland Security International.

Contact him at [email protected].