The MBA Gyrojet family are a series of weapons designed to fire the eponymous rocket-propelled smallarm ammunition. Produced during the 1960s-70s, they were intended to use rocket technology to reduce the weight and recoil of infantry weapons, but numerous shortcomings inherent to the design meant most variants saw little interest from military or civilian markets. The name is a portmanteau, combining the gyroscopic stabilization of the projectiles with the jet of rocket exhaust that propelled them.
History[]
The weapons trace their design back to designer Art Biehl's work on miniature armor-piercing rockets. To further develop this technology, Biehl joined with another designer, Robert Mainhardt, forming the company MB Associates, named for their initials.
The firearms were heavily promoted as a "space-age" weapon, with members of MBA approaching producers of various movies and TV shows in an attempt to have them featured: the most famous was Star Trek creator Gene Roddenberry, who is said to have liked the pistol but refused co-designer Nick Minchakievich's offer, as he wanted his fictional Starfleet to use a "ray gun." A more successful pitch was made to Eon Productions, resulting in Gyrojet pistols being heavily featured in the 1967 James Bond film You Only Live Twice.
Gyrojet weapons saw little military use with the only known case being by MACV-SOG operators in Vietnam: SOG purchased a number of pistols under the mistaken belief that they were silent. A noted user was First Lieutenant George Kenton Sisler, SOG's first Medal of Honor recipient. However, Gyrojet technology did find a use in the military in the form of the "pen flare," a small single-shot rescue flare launcher which replaced bulky break-open pistol-style flareguns in many military survival kits, particularly those used by aircrews.
The Gun Control Act of 1968 created a new legal term, the "Destructive Device." While the Gyrojet was below the limits for rocket propellant mass and had no explosive payload, it was affected by the Act's limitation of .5 inch caliber for any weapon not classified as a shotgun or flare launcher. To this end, a .49-inch Gyrojet variant was designed. The BATFE would later make an exception for the .51 Gyrojet, meaning that all .51 examples are fully transferrable without requiring NFA paperwork or a tax stamp.
As MBA teetered on the edge of bankruptcy in the 1970s with only around 2,000 weapons produced, Robert Mainhardt attempted a series of increasingly far-fetched pitches of possible applications of Gyrojet technology, including a Gyrojet-propelled speargun and even a proposal to use Gyrojets in space to attack Soviet satellites. None of these pitches succeeded, and MBA was bought out around 1980, with pen flare production being handed over to other manufacturers. Production of Gyrojet weapons and ammunition had already ended in 1975 when a fire destroyed MBA's production facilities.
Due to their general failure to catch on, Gyrojet weapons are extremely rare collector's items: despite their relatively cheap construction, even the most common models can often be found selling for over one thousand dollars. Ammunition is vanishingly rare on the civilian market with single rockets in presumed-functional condition fetching over two hundred dollars each.
Design[]
Gyrojet patent diagram, showing the main features of the unusual operating mechanism.
The main Gyrojet weapons are of lightweight design using Zamac, a zinc alloy, to reduce component weight, since the operating pressures are low and there is very little recoil due to the low launch velocity of the rockets. Most models featured an integral top-loaded magazine that has to be loaded one round at a time, with no provision for a stripper clip to speed up loading: this was noted to be a fiddly action since the integral magazine lacks feed lips and so the weapon could quite easily eject all loaded rounds if mishandled. Extraction of a dud rocket was also noted to be an awkward and slow operation, with a potential for injury if the rocket ignited while being removed.
Mechanically the Gyrojet is somewhat uncomplicated: since the entire projectile is fired with each shot, there is no need for any form of ejection or extraction. The actual action is extremely unconventional, effectively being a revolver-style hammer above the trigger which strikes rearwards, hitting the nose of the rocket to push it back against the striker, with the projectile itself forcing this hammer back into the set position as it moves forward. While some sources style this as blowback or blow-forward operation, neither is correct and the weapon's action is not described by any label applied to a gunpowder firearm. The weapon is initially cocked using a sliding lever that moves in a 90-degree arc, acting directly on the hammer. The barrel is smoothbore and the chamber is vented to disperse exhaust gasses directly out of the sides of the gun: presumably this is to stop the projectile's exhaust from venting into the integral magazine and potentially igniting the other rockets.
Similar concerns result in the incorporation of a unique safety feature in the barrel: since a stuck rocket would vent into the gun and potentially result in chain-firing or injuries to the operator from hot exhaust gases, the barrel is only attached with a small metal tab that is relatively easily detached. This means a stuck rocket will detach and eject the barrel out of the front of the gun.
The integral magazine's loading method differs slightly depending on the variant: the pre-production Model 137 and "A" variant guns have a fixed upper with a side loading gate, completely exposed on the Model 137 and covered with a flip-up side panel on the "A." The "B" variant switched to a moveable loading gate resembling a conventional pistol slide, which pulled back to the rear for loading.
Controls are only on the left-hand side in the "A" model: as well as the aforementioned cocking lever for the hammer, there is a tab running down the front grip panel edge which allows the operator to directly manipulate the magazine's follower and also acts as an indicator for the number of shots remaining, and a two-position safe-fire selector above and to the rear of the grip. The safety is a simple square switch with the "up" position raising a block in front of the striker, physically preventing the rocket's primer from being struck. In the "B" model an additional safety mechanism is added: the loading port can only be opened with the safety engaged, and the safety cannot be disengaged while it is open. The "B" model has an additional control on the right-hand side resembling a pistol's slide release, which is used to open the loading gate.
Pistol and Carbine versions are mechanically more or less identical, the latter simply being the pistol mechanism in a larger stock with a long barrel.
The weapons were noted for their poor accuracy, with even the manufacturer only claiming an accuracy of 17 minutes of arc, equating to 4.5 inch groups at 25 yards, mediocre compared to a conventional pistol (a military M1911 achieves around 12 MOA). Actual testing showed far worse accuracy in practice, with this discrepancy linked to errors in later production that produced rounds with one of the exhaust ports partially blocked. Even with ammunition that functioned correctly, however, the low muzzle velocity meant that extremely large deviations could be caused by minor movements of the weapon or any kind of wind.
Additionally, US Army testing found that the rounds were highly sensitive to moisture infiltrating the propellant through the open vents, which were equally prone to fouling. They were also generally unreliable, with an ammunition failure rate of at least 1% in testing, and were criticised for poor ergonomics, low capacity, disagreeably hot backwash from the rocket along with a tendency to vent rocket exhaust from the open grip during misfires, and the aforementioned awkward, slow reloading method, as well as the extremely high cost estimates for the ammunition.
None of these issues, however, were as fundamental a problem as the rocket itself. With the round accelerating over a 0.12 second burn time, it only had full energy at around 60 feet from the barrel, and as range closed the energy rapidly dropped to the point it could not be considered lethal: famously, the Bugs Bunny trick of sticking a finger in the end of the barrel would actually stop a Gyrojet projectile, though not to the extent it could be regarded as pleasant for the owner of the finger. Another issue unique to firing rockets was a slight delay between pulling the trigger and the rocket fully igniting: this delay meant a Gyrojet weapon could only fire around one shot per second regardless of how fast the trigger was operated.
Ammunition[]
Gyrojet ammunition showing exhaust ports. The one labelled "Gyrojet flare" is a pen flare round and could not be fired by the self-loading models.
The main family of Gyrojet weapons fired rocket-powered projectiles in .51 and .49 caliber, though experiments were performed with variants from as small as 6mm to as large as 20mm. While there are some misconceptions that they were explosive, Gyrojets were solid kinetic penetrators with the propellant being fully expended at a range of about 60 feet from the barrel. At this point the rocket, still weighing around 180 grains (11.6 grams) with the propellant expended, would have a velocity of around 1,250 feet per second (380 m/s), slightly above Mach 1, and roughly double the muzzle energy of a .45 ACP pistol round. Modern test-firings have found rocket velocity to be inconsistent with some remaining subsonic, though since all kinetic Gyrojet rounds in existence are almost fifty years old, it is unclear if this is due to production issues or propellant degradation.
Early experimental Gyrojets were notably extremely inaccurate due to a lack of any type of stabilization after leaving the barrel: they could not employ a rifled barrel as the rockets lacked sufficient velocity at launch to gain any meaningful stabilizing effect. Robert Mainhardt enlisted the assistance of a friend, Nick Minchakievich, to develop a solution. Experiments were made with 6mm and .51 rockets with retractable stabilizing fins, but it was concluded that this would increase the cost of ammunition too much and further work on this ammunition cancelled. Production Gyrojet rockets were instead spin-stabilized using a slightly canted angle of the exhaust vents, making them fire diagonally outwards rather than straight to the rear.
Early .51 rounds were of a two-vent design, which was later switched to four ports. Very late-production ammunition switched back to two ports as part of attempts to reduce production costs.
Pen flare launchers fired only a specialised flare projectile that could not be used in any other Gyrojet weapon: equally, the launcher could not fire any other type of Gyrojet projectile. Flare rockets were typically supplied in a plastic bandolier that held seven rounds, which was attached to the launcher with a lanyard.
Variants[]
Typical Gyrojet pistol presentation case with ammo caddy, bearing a bust of American rocketry pioneer Dr. Robert H. Goddard. This example is a Mark 1B.
Labels are somewhat confusing for Gyrojet variants since the "Mark 1" and "Mark 2" labels apply to both the carbine and pistol variants, describing whether they fire the older .51 caliber or newer .49 caliber. A and B model labels also apply to both carbines and pistols. Listed versions are those known to be more than mere ideas: a Rock Island Auctions article on Gyrojets states that Robert Mainhardt claimed he had no less than fifty potential applications for the technology, but most never proceeded beyond simply expressing it might be possible to do something with Gyrojets.
Model 137[]
Final pre-production prototypes. Cocking lever is circular rather than a tab, safety is smaller, rectangular rather than square and marked "on" and "off" rather than "safe" and "fire," and an additional takedown screw is present above the trigger. Unaltered versions have no loading gate cover, though some were modified to a pseudo-A standard with an added A-model loading gate. Sling loop at the rear is a small partial circle rather than integrated into a vertical line above the tang. Checkered plastic grip.
A Model[]
First production pistol/carbine variant with a left-side loading gate with a flip-up cover, easily identified by the lack of serrations for retracting the loading gate and two Phillips-head screws on the left side upper, one at each end of the flip-up loading port cover. Takedown screw is still present above the trigger. Criticized for being overly fiddly to load and difficult to unload.
B Model[]
Pistol/carbine variant with a redesigned loading method, the rear cover pulling back like a pistol slide to expose the integral magazine. Easier to load, but also with a much greater tendency to eject all loaded rounds if mishandled, since the only thing keeping ammunition in place was the user pushing the rear cover forward slightly between inserting rounds. Visible handling serrations on the lower part of the loading gate on both sides, and has a loading gate release on the right-hand side to the rear of the frame. No takedown screw is present above the trigger, but there is now one above the safety.
Pistol[]
Standard pistol variants, including the regular pistol, a snub variant, and the "survival pistol" which featured a retractable barrel for easier storage. Some Mark I pistols are refurbished pre-production Model 137s.
Carbine[]
Long-barrel variant with a rifle stock. Military-intended models (sometimes referred to as the "rifle" variant) had a carry handle, pistol grip, M16-style sights and angular furnishings with separate stock, handguard and grip panels, while the civilian "Sporter" models featured a scope mount, stainless steel barrel with a muzzle device of some kind and a more ergonomic rifle-style stock: this still had a pistol grip (due to the fixed magazine being inside it), but with a finger-grooved full wood grip rather than just side panels.
The military "B" model redesigned the stock and grip, introducing a taller and longer carry handle and a cutout in the stock so the B-model loading gate could be opened.
Survival 2000[]
Double-barrel break-open Derringer-style pistol. The weapon is a modified Rohm RG-17, with a .49 upper barrel made from a modified pen flare, and a .38 Special lower barrel. Less than 20 produced in the 1970s as part of a last attempt to save MBA from bankruptcy. A letter from Robert Mainhardt included in a presentation case with one example claimed it to be "one of a kind" in 1990.
Survival 2001[]
Second modified break-open Derringer model from the 1970s, this one made from a starting pistol and modified to fire Gyrojet flares from both barrels. Only 3 or 4 examples are known to have been made, with only one known to survive.
Lancejet[]
Muzzle-loaded speargun variant designed for use by Navy divers, with a Gyrojet propelling cartridge incorporated into the rear of each spear. Robert Mainhardt produced one aluminium example that he demonstrated in his backyard swimming pool, and designs for multi-shot variants, one with a revolver-style mechanism where each spear had its own barrel and a second 4-shot pepperbox-style launcher using electrical ignition. These do not appear to have progressed beyond diagrams, nor does the Navy appear to have been interested in the concept.
A/P25S-5A "Pen Flare"[]
All-service miniature single-shot flare launcher used in US military survival kits.
"Pepperbox"[]
12-barreled pistol produced for the film You Only Live Twice, but never used. Unclear if it was a functional firearm or a prop.
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