Small Rockets for the Masses?

Captain Monty Mendenhall  

Gyrojet  

          The ‘space race’ between the US and the USSR began in earnest in 1957.  The Soviet Union captured the high ground by orbiting the world’s first artificial satellite and reaped enormous national prestige.   

          In his recently published papers, the US’s number one rocket scientist of the cold war era, Wernher von Braun, stated that the US could have orbited a crude satellite in 1956 and beaten the Russians into space.  According to von Braun, political considerations prevented him from launching one. 

          An orbiting satellite would have unavoidably passed over the Soviet Union.  In 1957, the limits of a nation’s vertical airspace were undefined.  There was fear among US politicians, that an over flying US satellite would provoke a confrontation with the Soviet Union.  Von Braun felt that the order to put an orbiting US satellite on hold, came straight from President Eisenhower.

          After launching a satellite that over flew US airspace every ninety minutes, the Soviet Union was hardly in a position to be critical of future US satellite over flights of her own territory.  Four days after the successful Soviet satellite launch, US Secretary of Defense Quarles met with President Eisenhower and observed, “The Russians have in fact done us a good turn, unintentionally, in establishing the concept of freedom of international space.” (Quoted from Curtis Peeble’s  book, “The Corona Project”)

          Though allowing the Soviet Union be the first into space and reap world prestige humbled the US, the decision to delay the US’s first satellite was probably best.  Had the US launched the first artificial satellite, the USSR almost certainly would have protested and likely prevented, or at least forestalled future US satellite launches.  Another possibility, had von Braun been permitted to launch the first artificial satellite, the US would never have been perceived to be, ‘behind the Russians,’ and there would never have been the national enthusiasm that was required to support the tremendously expensive ‘space race’ which concluded with a US landing on the Moon.

 Discoverer

          The Discoverer satellite program was the first successful series of US satellites.  The program was aptly named too.  Under the cloak of scientific research, the primary goal of the Discover mission was to take high-resolution photographs of the entire Soviet Union.  Early in the program, there were many failures.  The first completely successful Discoverer flight was number 18 and what a success it was.  The data captured on that flight alone, was worth far more than the amount that the US had spent on the entire space program.  Discoverer 18 revealed that the much-vaunted Soviet bomber force was a hollow shell and that there were far fewer Soviet ICBMs than US experts had estimated.

          Discoverer 18 also photographed the launch complex at the secret Soviet space center.  These photos revealed a recent Soviet space disaster of enormous proportions.  It was evident that a huge rocket had exploded on the launch pad.  A photographic search of nearby cemeteries revealed many new graves.   It was years later though before the true extent of this Soviet disaster was revealed.  Among those killed in the accident was the commander of the Soviet Strategic Rocket Forces, Marshal Mitrofan I. Nedelin. Though a great loss, probably much more damaging to the USSR’s space program, was the death of Mikhail K. Yangel.  Yangel was the Soviet Union’s equivalent of the US’s Wernher von Braun.  Also killed were a host of government officials, rocket engineers and technicians.

          The data gleaned from Discover 18 revealed the USSR’s weaknesses and changed the US’s foreign and space policy forever.

 MBAssociates

          Almost lost in the excitement over the huge US space program, were the discoveries and developments of Robert Mainhardt and Arthur Biehl.  While most of the US’s rocketry research was concentrated on building larger and larger rockets, MBAssociates, Mainhardt and Biehl, were developing rockets that weighed less than one ounce.  They called their tiny 13mm (.51 caliber) rockets,  ‘Gyrojets.’

          Mainhardt wrote, ”In 1960, MBA expended a great deal of effort to prove that little rockets  – under one inch in diameter –  could be developed to be cost effective for various applications.  The world experts said it couldn’t be done.”

          One development was to ‘make a gun that could fire small rockets.’  We tooled up for a six shot, low cost, no recoil handgun that was foolproof and cheap.  These guns were die cast out of aluminum, magnesium or zinc alloy (except for springs and screws).”

          Mainhardt continued, “These guns worked and the unit cost was low, so you could give one to every Vietnamese farmer.  The late Vietnamese President Diem was given the first gold plated model.  He then gave his ‘village chieftains’ silver plated ones.  The ‘village chieftains’ were to give every farmer a plain one. Then, guess what?  The working farmers didn’t want them.  They said, ‘Why should we shoot the Viet Cong?  They only come to get their ‘tax ration’ of rice.  We know we will either have to give them some rice or give some to Saigon, so who cares?’ ”  

Thus ended the “Rocket Guns For Rice Farmers” program.

 More MBA Developments

          Robert Mainhardt continued, “Many other products (besides the rocket guns) were devised from the early efforts of Art Biehl and myself.  We built some seven million signal flares using the Gyrojet rocket engines.” In addition to the Gyrojet pistol, MBA also developed and marketed Gyrojet carbines, Gyrojet inserts for 12 gauge shotgun barrels and Gyrojet underwater spear guns.

          Though the 12mm Gyrojet rockets were made in the greatest quantities, other calibers were made as well.  These Gyrojet calibers included .16, .25, .30, .38, 13mm, 20mm, 30mm and 40mm.

          Because Gyrojets are rockets, they place little stress on the launcher and have almost no recoil.  A Gyrojet launcher for the largest 40mm ammo could be lightweight.  Firing one from the shoulder in either the semi auto or full auto mode would be both possible and practical.

Area Saturation

          Mainhardt added, “We also made hundreds of thousands of fin stabilized rockets (called MBA Finjets) of under 1/8 inch diameter (1.5 inch length) that flew at Mach 2 (1400 mph).”

          The original purpose of the tiny Finjet was to saturate an area with high kinetic energy projectiles.  This concept was never fully explored.  The MBA Finjet may have been the inspiration though, for a weapon once used in a ‘James Bond’ motion picture. No actual connection is known, but Bond’s ‘last ditch cigarette rocket weapon’ looked much like an MBA Finjet. 

 Stabilization Differences

          Gyrojet rocket ammo and Finjets are stabilized using different principles. The Gyrojet has no fins.  Having no external projections makes it more suitable for use in a magazine fed weapon. To stabilize it, the Gyrojet must have two or more rocket nozzles.  The nozzles are canted to impart a stabilizing spin to the small missile. A standard 13mm Gyrojet rocket rotates at about 3600 revolutions per second (216,000 rpm).

          Simplified fin stabilized Finjets only required one rocket nozzle. Though no cost figures have been revealed, it was likely the less expensive of the two rockets to manufacture.

          Even smaller and simpler than the fin stabilized MBA Finjet is the 1/16 inch diameter, 1.5 inch long, MBA Lancejet.  Like an early Chinese skyrocket, with a long stabilizing stick instead of fins, the tiny MBA Lancejet’s length stabilizes it to some degree.  As for its intended use, Mainhardt states, ”Multiple salvos of these lower velocity subminiature rockets exhibit characteristics similar to Finjets, but elimination of the fins provide unique advantages.” 

          Left unstated by Mainhardt (perhaps due to ongoing research), are the specific advantages of the Lancejet. One potential use for the finless Lancejet would be as ammo for a very high speed Gatling gun type of rocket launcher. With low weight and little recoil, a weapon of this type could be mounted on a light utility vehicle or a small helicopter.  This type of weapon might be ideal for area saturation.

 Classified New Uses?

          MBA developed larger versions of the Lancejets.  Mainhardt described them as, “Javelin stabilized rockets with excellent penetrating and warhead carrying ability.  Payload volume is sufficiently large to carry an impressive explosive or incendiary charge, capable of inflicting substantial primary damage and able to detonate explosive or inflammable targets to produce secondary damage.  Lancejets pack like simple rods.”

          In 1980, Mainhardt proposed a method to protect ICBM silos with a system called ‘Swarmjet.’  An excerpt from his proposal stated, ”Our most significant force deficiency… will be the vulnerability… of our fixed silo ICBMs. … There is a solution called… called Swarmjet… using large numbers of relatively small high velocity rockets fired in salvos to ‘kill’ incoming ICBMs.”

          Further, but classified, work may still be being going on with larger versions of MBA Finjets and Lancejets.   A large salvo of tiny rockets might be an effective final, very close range, defense against anti-ship missiles.  Another use might be for intercepting an incoming ICBM at high altitude, before it could release its MIRVs.  The final stage of the anti-missile missile would launch a salvo of thousands of tiny rockets toward an incoming MIRV platform.

  Simple Rockets
With Complex Technology

          A Gyrojet rocket consists of eight components.  The largest is the hollow rocket case.  It is made of high tensile strength steel to withstand the 2500 psi of internal pressure caused by the very hot combustion gases and the high centrifugal forces caused by rotating at 3600 revolutions per second.

          The second component of the Gyrojet is the base.  The third and fourth components are contained within the base. In the center of the base is a percussion primer.  Arranged symmetrically on the outer perimeter of the base are two, or more, rocket nozzles.  The nozzles are canted to impart a stabilizing spin to the rocket.  The spin is calculated to be three turns per foot of linear travel.  In rifle barrel terms, this would be a very fast twist ratio of one turn in four inches.

          TThe Gyrojet’s nozzle material must have a precisely defined erosion and ablation rate.  If the nozzles burn or erode unevenly, asymmetrical thrust will be produced.  If that occurs, the rocket will become destabilized, destroying its accuracy.

          The fifth component is the propellant.  Solid rocket propellant containing metal, and therefore having a high density, can give high thrust. Due to safety considerations however, Gyrojet rockets use a propellant that is quite similar in composition to double-based nitro cellulose gunpowder.  Mainhardt stated, “Non-metalized double-based propellants (gunpowder) cannot detonate (explode).  They can only deflagrate (burn).  A composite or metalized propellant is probably unsuitable for use in a hand held weapon.”

Another consideration for choosing a double-based nitrocellulose propellant instead of a metalized one, is that the combustion gases of gunpowder type propellants are relatively clean and non-toxic.  The combustion gases of metalized propellants are both corrosive and toxic. Neither trait is desirable, especially for indoor defense use.

          Cost benefits also resulted from using a double-based nitrocellulose propellant instead of a metalized one.  Gunpowder type propellant is much less expensive than the metalized type.  Moreover, the metalized propellant is very erosive.  Rocket nozzles for gunpowder type propellants can be made from cold rolled steel. Metalized propellants require the use of more expensive nozzles that are made of ceramic or from other exotic materials.  

          Gunpowder type propellants are relatively simple and safe to work with. Using ‘dowling’ and ‘pencil sharpening’ machinery, MBAssociates formed the double-base nitrocellulose powder into pointed cylinders. These cylinders of propellant closely fitted the inside of the steel rocket case. 

          Primer ignition alone was insufficient to ignite the rocket propellant quickly and uniformly. The sixth component of the Gyrojet  rocket was a sensitive chemical ‘initiator.’ The ‘initiator’ received the initial impulse of the primer and ignited the propellant. To accommodate the ’initiator’ and to provide a path for the combustion gases, the cylinder of rocket propellant was formed with a tube-like hollow cavity in its center.  The ‘initiator’ was placed inside the hollow tube.

          To help reduce the rocket’s internal pressure, a seventh component, a combustion inhibiting chemical compound, was applied to the outside of the propellant cylinder.  In this way, the propellant could only burn from the inside. The inhibitor prevented it from burning on the outside and raising pressures to unacceptable levels.

          Data provided by MBA states that the maximum thrust of the gunpowder fueled Gyrojet, is 3.2 kilograms or approximately 7.5 pounds.  This may not seem like a lot of thrust, but when applied to a missile weighing only 185 grains, the thrust to weight ratio is an astounding 284 to 1. For comparison, the combined thrust of a Boeing 777’s engines is 180,000 pounds.  The maximum takeoff weight is 640,000 pounds. A Boeing 777’s thrust-to-weight ratio is only .281 to 1, about 1/1000th of a Gyrojet rocket’s. 

          Like a B777 on take off, a Gyrojet rocket begins moving relatively slowly.  The Gyrojet’s fuel burns for 1/10 of a second.   When its fuel is consumed at sixty feet downrange, the unguided missile has accelerated to a velocity of 1250 feet per second (FPS), slightly greater than Mach one.

          The last component the Gyrojet rocket ammo is an aluminum membrane.  It is located between the nozzles and the propellant. The membrane seals the case to prevent the entrance of moisture.  The primer and the internal pressure after propellant ignition ruptures the membrane, permitting the burning gases to escape through the rocket nozzles.

 

Wernher Von Braun

          Mainhardt kept Wernher von Braun informed of MBA’s research into small rockets. Von Braun replied with the following comments. 

          “I have read with interest…. the report that you recently sent me.  The considerations in this very thorough treatment of miniature rocketry are reminiscent of some of the problems we are encountering in our daily work, although essentially at the opposite ends of the size spectrum.  The progress you have made in proving feasibility and usefulness of these little rockets is noteworthy.  I foresee many valuable applications in the weapons field.”

 

The Gyrojet Launcher

          Looking much like a semi automatic pistol, the seventeen-ounce Gyrojet rocket launcher is cast from zinc alloy or aluminum.  The only precision made part is the extruded launching tube or barrel.  For accuracy, a very close fit is needed between the Gyrojet rocket and the barrel.

          Standard MBA Gyrojet pistols have a five-inch barrel.  A few snub nosed models were made with two-inch barrels.  MBA also manufactured carbine style launchers for Gyrojet rocket ammo.  The operating mechanisms of all three are identical. 

          The velocities of the snub nosed pistol, the five-inch barreled pistol and the carbine type launchers were identical.  This is easily explained.  Unlike normal cartridge ammo, the barrel length has no effect on the velocity of Gyrojet rocket ammo.  Most of the Gyrojet rocket’s acceleration takes place after it has exited the launching barrel.

          To be accurate, the Gyrojet rockets must fit the bore of the launcher very closely. Twenty-four Gyrojet 12mm rockets were measured. They were very consistent.  All measured .496 X 1.400 inch, plus or minus .0005 inch.  The tube’s inside diameter measured .499 inch. The average clearance between the launching tube and the rocket was only .0015 inch. Since the Gyrojet rocket is self-stabilizing, the tube requires no rifling.  The diameter of 13mm Gyrojet ammo is .511 inch.  Like the 12mm ammo, its diameter was very consistent also.

          The Mark I and Mark II Gyrojet launchers are much alike. Both hold six rounds of rocket ammo in their grips.  They do not have detachable magazines.  The most noticeable differences are their methods of ‘loading’.  The Mark I is loaded through a port on the left side of the launcher.  A cover swings vertically to access it.  The Mark II has a retractable ‘slide’ over its ammo well. The slide is retracted to load a MK II launcher.

          To load either launcher, first lower the hammer and place the safety to ‘ON.’ Next, open the loading gate (Mark I) or retract the ‘slide’ (Mark II) and press six of the Gyrojet rockets downward into the grip. The follower is spring-loaded.  Be careful.  All of the rocket rounds will pop out of the grip if the loader’s thumb slips off of the top round.  Finally, while restraining the rockets, close the loading gate or  ‘slide.’

 

Multi-purpose Hammer

          The Gyrojet’s hammer is located in front of the trigger.  Before firing the first round, cock the hammer forward and down.  When the trigger is pulled, the hammer moves up and backward.  It strikes the nose of the rocket and forces the primer against a fixed firing pin that is located behind the rocket. 

          The Gyrojet launcher’s safety restrains neither the hammer nor the trigger.  If the trigger is pulled when the safety is ‘ON,’ the hammer will strike the rocket.  The rocket will not ignite however.  When the safety is ‘ON,’ a metal block moves up between the rocket and the fixed firing pin, protecting the primer.

          The backward striking hammer is an inspired feature that simplified launcher production and reduced costs while simultaneously solving a major problem that is associated with spin stabilized rockets.  Since the hammer strikes the rocket on the nose, it blocks the exit path of the rocket.  When the rocket moves forward, it recocks the hammer.  This simplifies the design and permits a quick second shot.

          To achieve a reasonable degree of accuracy, a spin stabilized rocket must be allowed to ‘spin up’ before it exits the barrel. The  rearward pressure that is generated by hammer spring on the nose of the rocket, restrains the rocket briefly to allow time for it to ‘spin up.’  Without the restraint of the hammer, the Gyrojet rockets would leave the snub nosed and five-inch barrels before they became stabilized. Without the hammer’s brief restraint, there would be no hope of accurate fire. 

 Low Volume Causes
High  Production Costs

          Gyrojet rocket launching pistols were inexpensive to produce. In 1970 their retail price was $99.00 though.  For a gun that was produced with a level of technology that was similar to making a cap pistol, that was a high price.  At that time, for comparison, the price of a S&W Model 10 revolver was about $100.00. 

          Manufacturing Gyrojet rocket ammo was another matter entirely. It was expensive to produce.  The first batches were made by hand using machine tools.  In 1965, it was priced at $1.35 per round.  By 1972, the retail price had increased to $3.00 per round.  Unverified by Mainhardt, but many RKIs feel that even at $3.00 per round, the rocket ammo was sold at a loss.  By the late 1970s however, there was little demand for Gyrojet rocket ammo.  Norbert Smoot, a longtime FFL/SOT dealer, recalls “…seeing pallets of Gyrojet ammo priced a $1 per box of six” at Davidson’s  Wholesale in Greensboro, NC.

          Had Gyrojets achieved popularity and high production rates, the ammo costs would have been more reasonable. Robert Mainhardt maintained that, “Cost analyses showed that miniature rockets and conventional ammo would cost about the same if produced in the same quantities. ….both are fabricated of similar materials  - steel, double-based propellants, primers -  and both require approximately the same number of operations to the same tolerances.  It is possible that future Gyrojet designs could be produced at less cost than conventional ammunition.”

          Unfortunately, conventional ammo is produced at the rate of billions of rounds per year, while Gyrojet ammo was produced at less than one million rounds.  There was little economy of scale for Gyrojet production.

 Gyrojet Performance

          According to data published by MBAssociates, standard 12mm Gyrojet rockets weight 185 grains and achieve a burnout velocity, at sixty feet down range, of 1250 fps. Their energy at the propellant burn out point is 700 foot-pounds, approximately twice that of standard .45acp 230 grain ball ammo.

          Early Gyrojet rocket production suffered from a lack of quality control.  H. P. White Laboratories tested a batch of it in June of 1963.  About 20% of the rockets failed for various reasons.  Accuracy was unacceptable as well.  Initial dispersion averaged 20 mils of circular error probability (CEP).

          A second batch of 98 improved Gyrojet rockets was tested later that year.   Three of them failed to ignite and seven more of the 98 rounds required a second blow from the hammer before igniting.  Accuracy improved to 7 mils CEP or about 7 feet at 100 yards.  Though better than the first tests, this must still be regarded as unacceptable performance.  One in ten rockets failed to ignite on the first try.   Mainhardt later claimed to have reduced the failure rate to only 1%. 

Gyrojets and
The National Firearms Act

          Gyrojet rockets are spin stabilized by their canted nozzles.  Hence, they require no rifling.  Early Gyrojet pistols were smoothbore.  As soon as the BATF (Alcohol, Tobacco Tax Unit, or ATTU, in 1963) noted that the Gyrojet handguns were smoothbore, they required that their bores be rifled to avoid being classified as Title Two ‘Any Other Weapons’ (AOW).  

          After the ATTU’s ruling, MBA engraved their new Gyrojet launcher barrels with very shallow rifling to avoid the AOW classification.  A Gyrojet rocket does not engage the rifling.  It will drop freely through the bore. The rifling serves no purpose at all except to avoid the AOW designation.

 

Destructive Device Gyrojets

          Gyrojets were developed before the 1968 Gun Control Act was passed.  Among other things, the 1968 law created a new firearm category for firearms with a bore diameter greater than fifty caliber, Destructive Devices (DD).  Prior to its passage, a live cannon could be bought with no more difficulty than buying a rifle.  Many firearm magazines from the early 1960s contained ads from Potomac Arms for wheeled cannons.  Readers were urged to ‘buy one and tow it home.’

          A 13mm Gyrojet’s bore diameter is greater than .50 caliber.  It is .511 inch.  That created a problem for many who had legally bought 13mm Gyrojets prior to the passage of the 1968 Firearms Act.  If they had missed the 1968 amnesty registration of them, they were in possession of unregistered Destructive Devices.

          Acting very responsibly, MBAssociates requested and received permission from the Alcohol, Tobacco and Firearms Division of the Internal Revenue Service (the name of the BATF in 1970) to convert the previously sold, unregistered, 13mm Gyrojets to 12mm, or, .49 caliber, thus removing them from the DD category.

          In 1981, BATF ended the 13mm Gyrojet problem entirely by removing them from the DD category and classifying them as ‘Curios & Relics.’  Edward M. Owen, the chief of the BATF’s technical branch, wrote a letter to Bob Mainhardt to notify him of this change. The letter is reproduced below.  Owen’s letter also confirms that some Gyrojets were full auto. 

          This article is based on letters and interviews with Robert Mainhardt that were recorded in 1992, plus data published by MBAssociates and data from the collections of Kevin Dockery, Leonard Yates and Tim Bixler.  Unfortunately, the author has lost contact with Mainhardt and could not ask him any questions about the full the auto versions of his Gyrojet rocket launchers. 

          Tim Bixler, the co-developer of the ‘stealth’ radio submachine gun was able to supply some interesting anecdotes about the full auto Gyrojets.  See the accompanying interview for more information about his full auto Gyrojet and the thirty day, 1968 amnesty registration.

 

The BATF Letter

Dear Mr. Mainhardt: 

This refers to your letter of March 25, 1981, in which you provided information regarding the production of Gyrojet Rocket Guns.  For your information, the following firearms have been have been removed from the destructive device category and are no longer subject to the provisions of the National Firearms Act (NFA):

 MBA Gyrojet Rocket Guns, caliber 13mm,
semiautomatic version only, produced in 1968 or earlier,
serial number ranges  A0001 through A0032, A001 through
A085, B010 through B411, and B5059 through B5692. 

The above firearms have also been determined curios or relics as that term is defined in Title 27, Code of Federal Regulations (CFR), Part 178, Section 178.11, thereby authorizing licensed collectors to acquire, hold, or dispose of them as curios or relics subject to the provisions of Title 18, United States Code (U.S.C.), Chapter 44, and the regulations in Title 27, CFR, Part 178.  They are still firearms as defined in Title 18, U.S.C., Section 921 (a) (3).

Persons having registered firearms in the above category should write the NFA Branch and request that their file in the National Firearms Registration and Transfer Record be amended to reflect that these firearms are no longer subject to registration requirements.

                        Sincerely yours,
(signed)          Edward M. Owen, Jr. 

 

Modern Tests

          Little has been written about MBA Gyrojets.  The few stories that have appeared have, for the most part, simply repeated data that was supplied by MBA.