Make: MB Associates (MBA)

Model: Based on features, this appears to be an experimental version of the Mark I, see Our Assessment.

Serial Number: None.

Year of Manufacture: Ca. 1963-1965

Caliber: 13mm Gyrojet, a 13mm spin stabilized rocket cartridge composed of four part solid rocket fuel. (ATF Exempt, non-Destructive Device)

Action Type: Semi-Automatic with Fixed Magazine

Barrel Length: 6 3/4"

Sights / Optics: The front sight is a blade fixed to the barrel portion of the frame at the muzzle. The rear sight is missing.

Stock Configuration & Condition: The grips are two-piece smooth wood screwed to the sides of the frame. The grips have scattered light nicks and scratches. There are no chips or cracks. Overall, the grips are in about Very Good condition.

Type of Finish: Black

Finish Originality: Original

Bore Condition: Rather than a traditional barrel, the frame has a hollow tube integral to the frame. Model 137 pistols had integral guide-rails, Mark I pistols had a separate tube mounted inside the frame. This example has neither. The bore shows signs of firing, but no erosion or damage. In this writer's opinion, the bore rates 8+/10.

Overall Condition: This pistol retains about 87% of its metal finish. The finish is thinning at some edges. There are scattered nicks, scuffs and scratches. There is oxidation and erosion on the firing pin and safety block. There is finish wear on the loading door and there is a void in the finish of the firing pin block where the rear sight was mounted. The screw heads are tool marked with strong slots. The markings are clear. Overall, this pistol is in Good-plus condition (see Mechanics).

Mechanics: The safety will not engage, likely due to erosion on the block. Otherwise, the action functions correctly. We have not fired this pistol. As with all used firearms, a thorough cleaning may be necessary to meet your maintenance standards.

Box, Paperwork & Accessories: None.

Our Assessment: Who doesn't want a hand-held rocket launcher? MB Associates thought the answer would be "everyone!". Robert Mainhardt and Arthur Biehl met while working together at Aerojet-General Nucleonics, working on their AGN-201 nuclear reactor. While MBA was profitable in their manufacture of chaff and flare devices for aircraft, the Gyrojets would have to be considered something of a passion-project.

The cartridge design actually hearkens back to one of the earliest self-contained cartridges, the rocket-ball. With all of the propellant contained in the cartridge, a fixed firing pin is ignited when the hammer strikes the front of the cartridge. Once ignited, the burning propellant comes out of angled ports at the rear of the cartridge, spinning the entire assembly to stabilize it as it accelerates down the bore. Unlike traditional cartridge firearms, the projectile continues to accelerate for up to 20 yards after leaving the bore, reaching its highest velocity not at the muzzle, but when the propellant is exhausted. Quieter than a traditional cartridge, the firearm could be made extremely light as it did not have to contain much pressure, and it would work under water (in theory).

This example is something of a mystery due to its features. It has a 13mm bore that is integral to the frame, having neither the tube insert typical of the Mark I pistols nor the guide-rails of the earlier Model 137. It has a swing-up loading door found on the Mark I, but the lug under the barrel has deep recesses and the pistol is overall notably lighter than a standard Mark I. Perhaps most notable is the construction, which has a typical two-piece frame, but has a separate block pinned at the top-rear to mount the firing pin. Moving parts on the 137 and Mark I are secured by internal pins integral to the frame halves while this pistol has bushed pins that go all the way through the frame. All signs point to this being some sort of experimental or prototype piece to explore different methods of construction for a Gyrojet pistol.

With about 1,900 Gyrojets produced in all of their pistol and carbine configurations, any example is a good find. This example's unique features will make it a great addition to a collection that already has a few Gyrojets, and there likely are few if any more like it. Please see our photos and good luck!