A rocket gun, what Buck Rogers fan could resist?

Stroboscopic photo turns the bullet's exhaust into a line of red circles. The firer can see the bullet's exhaust, but the target cannot.

The good old MBA Gyrojet pistol (1968) is worth looking at. This out of production weapon actually fired rocket bullets. The tail jets were angled to spin the rocket bullet in lieu of rifling. Conventional rifling in the barrel cannot be used since rocket bullet does not have enough initial energy.

In Gordon R. Dickson's Dorsai novels, they were called "cone rifles." This was borrowed for the miniature game Space Marines, and from there it spread to the RPGs Space Opera and Paranoia.

If you want all the details, go read the definitive Gyrojet article at Future War Stories.

It had some advantages:

It had practically no recoil, about 1/10 th a Colt M1911 (but alas, as we saw, recoil isn't a problem in freefall).

a Colt M1911 (but alas, as we saw, recoil isn't a problem in freefall). It is more quiet than a conventional firearm. It makes a soft noise comparable to the "pfhsssssssst!" sound of opening a can of carbonated beverage. It does make a "crack" nose when the round goes supersonic; but this happens far in front of the firer, not right at the muzzle.

The weapon is low mass, since the barrel is never pressurized the firearm can be made out of lightweight alloys or even plastic. The original model was made out of an inexpensive zinc alloy called Zamak. A naive target glancing at a threatening Gyrojet might mistake it for a child's toy, at least until the rockets started flying.

The firing mechanism has fewer moving parts than a conventional weapon so therefore is less prone to jam. Fewer parts also allows higher firing rates.

Most of the bullet's propellant is burned during flight outside of the weapon, with much less heat build up. This as well allows higher firing rates, up to 60 RPM.

Since the precision and high-pressure parts are all in the rocket shell, the weapon itself can be constructed out of low precision die-cast or stamped parts. This also simplifies field repairs. It also has the result of making the weapon relatively inexpensive but the ammunition more expensive.

The rocket propellant is clean burning leaving little or no residue. Hundreds of rounds can be fired before the weapon requires even minor cleaning.

The flame of the rocket is only visible from behind, so while the firer can see it the target cannot.

They work underwater much better than a conventional bullet

click for larger image

click for larger image

click for larger image

click for larger image

Problems included slow burn times. This meant if your target was too close, the bullet didn't have enough time to get up to a speed capable of damaging it. If the target is only 0.3 meters or closer the bullet will probably limply bounce off, fall down, and spin on the ground spitting sparks like a dud firework. The bullet only got up to full speed after it had traveled about 9 meters, which is a bit excessive. Especially considering that average range of a confrontation with a handgun is about 2 meters. At that range a gyrojet round would have a pathetic penetrating power of about 80 joules, about the same as a .22 Rimfire Short cartridge.

For these reason some say the Gyrojet should have been marketed as a long-arm rifle, not as a pistol. The problem could be fixed if a faster burning propellant was subtituted.

The MBA Gyrojet also had poor accuracy. As it turns out, that was due to the MBA ammunition, not because rocket bullets are inherently inaccurate. The MBA ammo suffered from shoddy manufacturing and poor quality control. The main problem was that the bullet's nozzles were not aligned with each other, forcing the rocket off target. The fact that 1% to 10% of MBA's manufactured rockets would misfire didn't help either.

But with some development, the weapon might be redeemed. The Deathwind project is attempting to create the next generation of gyrojet weapons. Or if you prefer the brute-force approach, the rocket bullets could be enhanced with explosive warheads or made into radar-guided missiles, heat-seeking missiles, or smart bullets.

Coridon Henshaw suggests special fusing for the explosive warheads, so the shaped charge will go off if they contact flesh or body armor, but not if they hit the hull. He says another possibility is a multispectral sensor and sighting laser that will disallow firing if the line of sight ends at something that is part of the spacecraft. Include a manual override in case some diabolical space pirate figures out how to make their body armor look like hull plates.

The pistol had a mass of 0.4 kg (as compared to the Colt M1911 with a mass of 1.1 kg). The over-all length was 27.6 centimeters, with the barrel being 13 cm. The pistol holds six rounds in the magazine, which was regrettably not a removable magazine. The weapon had to be loaded by opening the bolt and feeding rounds into the magazine one-by-one, which made quick reloading impossible.

Rocket bullets



Gyrojet

Round Charge Weight Max Vel Dmg 13 mm Standard (@2m) 2.9 g 12.0 g 80 j 13 mm Standard (@9m) 2.9 g 12.0 g 380 m/s 950 j 13 mm High Velocity 7.1 g 7.1 g 700 m/s 1690 j 13 mm Heavy Weight 0.9 g 20.1 g 120 m/s 150 j 13 mm Target 0.2 g 7.1 g 120 m/s 50 j 13 mm Std Long 4.5 g 17.8 g 450 m/s 1900 j 20 mm Standard 6.5 g 43.7 g 330 m/s 2580 j Conventional

Round Weight Max Vel Dmg .22 Short 1.9 g 340 m/s 80 j 9mm (Luger Parabellum) 7.5 g 350 m/s 450 j .45 ACP (Colt M1911) 14.9 g 260 m/s 500 j .38 Special 9.7 g 320 m/s 520 j .357 Magnum 10.2 g 430 m/s 940 j .44 Magnum (AutoMag) 15.6 g 450 m/s 1560 j

Each .50 caliber rocket "bullet" had a mass of 9 grams (6.65 grams of rocket + 2.5 grams of propellant). The most common rounds were 13mm (0.51 caliber), though others ranged from 2.8mm to 40mm. Each rocket has a low velocity at the point where it exited the muzzle, but by the time it had traveled 9 meters (0.12 seconds after ignition) the propellant had all burnt and the round had accelerated to its full velocity of 380 m/s. The kinetic energy delivered to the target was about 950 joules. By way of comparision a Colt M1911 .45 ACP bullet delivered from 477 to 835 joules and an AutoMag .44 Magnum bullet delivered between 1000 and 2000 joules. However, as previously mentioned, at a range of 2 meters (average range of a confrontation with a handgun) the round would only be fast enough to deliver a disappointing 80 joules.

Effective firing range was about 50 meters. Keep in mind that if the rocket hits something before the propellant is spent, the 5000° F exhaust might ignite the target.

The propellant was a double-based nitrocellulose propellant. These cannot explode, just burn. A composite or metalized propellant was rejected because the magazine would tend to explode if you dropped the weapon or box of ammo. The latter propellants also had toxic and corrosive exhausts, another reason to reject them. The double-based nitrocellulose propellant charge in the round produced a maximum thrust of 33 newtons. The thrust-to-weight ratio was about 284 to 1. The rocket accelerates at something close to 600 gs.

The final advantage of double-based nitrocellulose is that it is smokeless. However, on a cold day the rocket will leave a contrail of condensation.

The angling (port angle) of the rocket exhaust jets is a tricky design task. It divides the rocket thrust into two components: forwards thrust and angled thrust. The forwards thrust propels the bullet towards the target to inflict damage, the angled thrust spins the bullet for gyro-stabilization. The problem is deciding how to divide the thrust between the two components. Too much angled means too little bullet velocity delivering damage to the target. In addition too much angled could spin the bullet too rapidly, causing it to actually disintegrate in midair due to hoop stress. But if too little of the thrust is angled there will be not enough spin for proper gyro-stabilization. Most gyrojet rounds have a port angle of 15°, so 85% of the thrust was in forwards motion and 15% was used for spin. The standard gyrojet round spins at a rate of 3600 revolutions per second (216,000 rpm).

Nowadays designers would probably not bother to use spin gyro-stabilization at all, instead they use smart bullets.

The rocket's case is made of high tensile strength steel to withstand the 17,000 kilopascals internal pressure from the propellant, and the hoop stress of spinning like a top on steroids at 3600 rps. MBA was experimenting with a Gyrojet "shotgun round", where a wad in the nose would hold the pellets, and the wad designed to disintegrate under hoop stress and internal propellant pressure.



Note cocking lever in semi-circular groove to the left. Lip at top of walnut handgrip forced thumb to be straight and low, so as not to be damaged by the cocking level when the trigger is pulled.

Safety switch is on right. The row of holes are exhaust ports.















The Gyrojet did have a remarkably jam-proof design, due to the small number of moving parts. Instead of a movable firing pin struck by a hammer, there is a fixed pin at the back of the chamber. The hammer strikes the front of the rocket, forcing it back onto the fixed firing pin. The rocket's primer strikes the firing pin, igniting the rocket's propellant. The rocket shoots out the barrel, simultaneously re-cocking the hammer (this steals about 10% of the 13mm std rocket's energy). The hammer is initially cocked by thumbing a lever on the side of the sidearm, in an arc-like groove above the trigger. The cocking lever is on the left side of the weapons, which makes it awkward for left-handed people.

A lip at the top of the walnut handgrip forces the thumb to be straight and low. Otherwise when the trigger is pulled, the cocking lever on the hammer will slam up and injure the hapless user's thumb-tip.

Once the hammer forces the rocket onto the firing pin, it also momentarily restrains the rocket in place. This gives the rocket a chance to "spin up" enough to be gyro-stabilized. Otherwise the rocket would emerge from the barrel unstabilized and accuracy would be impossible.

Unlike conventional designs, the Gyrojet firing mechanism does not need a reciprocating bolt, an extractor, or an ejector. This results in a much lower part count for the firing mechanism, and far fewer ways to jam. The firing mechanism requires no lubrication, and will still operate if the weapon is contaminated with dirt, mud, or other debris.

Note how high the barrel is mounted above the trigger, compared to a Colt M1911. This is to accommodate the internal hammer.

The weapon's safety switch raises a metal obstruction to cover the firing pin. Unlike a conventional safety, it does not lock the hammer and trigger, which is a rather unreliable solution.

Misfires were a problem as well. You could either manually re-cock the hammer and try again, or open the slide and remove the defective rocket. Be careful opening the slide, the magazine spring will try to eject all the rockets like a jack-in-the-box. Also be careful opening the slide because if the defective rocket is a hangfire, it will suddenly launch into your face (owner's manual recommends a ten second wait). The MBA Gyrojet design could use some improvement.

A gyrojet barrel should be smooth-bore, no rifling is required. MBA put decorative rifling in anyway because of a stupid provision of the 1962 National Firearms Act would have added a tax on the weapons (with no rifling a gyrojet would be classified as Title Two 'Any Other Weapons'). The Mark I gyrojet rounds were 13mm or 0.511 caliber. This would run afoul of the 1968 Gun Control Act, which classifies weapons with a bore diameter greater than 0.50 caliber as "Destructive Devices." MBA responsibly got permission from the BATF to convert unsold 13mm gyrojets into the Mark II version with 12mm rounds, or 0.49 caliber. Later the BATF fixed the problem by classifying gyrojets as "Curios & Relics".

Gyrojet carbines. But if those holes behind the barrel are exhaust holes, doesn't it incinerate the user's face? No, the initial rocket blast is more like a warm wind than it is a blowtorch.









Designer Robert Mainhardt risks his nose to demostrate the lack of recoil

What caused the MBA company to go bankrupt was the fact that the military didn't want the Gyrojet, and there was no civilian market for a weapon whose ammunition costs over a dollar a shell (about six dollars a shell in 2015 dollars), with no possibility of re-loading the shells.



















There was a a 12mm gyrojet underwater spear gun (called the Lancejet), a snub-nosed survival gyrojet pistol, and an over-and-under derringer modified to accept a gyrojet round in the upper barrel. Like the original gyrojet none of them caught on either. There was also an insane experiment with a "volley gun" variant, which simultaneously fired 12 nine-millimeters rockets with one pull of the trigger.

(ed note: this is not from a novel, this is reality. Tim Bixler purchased his first gyrojet in 1965.) I once took my Gyrojet out there, number 67, and the scuba gear. I jumped off of the police boat and went down about, I don’t know, five or ten feet, and I shot the Gyrojet underwater. It was really, really neat. The bullet went out but it left a spiral trace of bubbles from the four rocket nozzles. As the rounds got farther out, I imagine about five or ten feet, but this has been a long time, the bubbles expanded. When I looked where the round had been, and I have no idea how far it went but probably not too far after the burn out, the bubbles kind of expanded. It was kind of like looking down the big end of a megaphone. That’s the best way I can describe it. As they were expanding, they were also deforming. The bubbles were trying to float up. I can’t describe it better than that, but boy was it neat. After shooting a few rounds like that, then, from about five feet under water, I shot a couple up into the air. They went to the surface but the bubbles didn’t deform the same way. Since they were going up, the spirals stayed round. You probably don’t care about all this but it was neat and I am reliving all this in my mind as I tell it. Anyhow, after I shot five or ten more rounds, I came up and my partner on the boat said, “Man! What were you doing?” I said I was just playing with this gun I got. He said, “Things were coming out of the water going 'phew' up in the air.” It put me in mind of the atomic submarines launching missiles. I know that’s an exaggeration but it was neat. From Gyrojet Recollection of Tim Bixler, by Captain Monty Mendenhall

Gyrojet pistol from TSR's role playing game Star Frontiers.

Artwork by Dick Calkins for Buck Rogers 2432 A.D. newpaper comic strip June 6 and 7, 1929. Images from Roland Anderson

Rocket guns are very simple contrivances so far as the mechanism of launching the bullet is concerned. They are simple light tubes, closed at the rear end, with a trigger-actuated pin for piercing the thin skin at the base of the cartridge. This piercing of the skin starts the chemical and atomic reaction. The entire cartridge leaves the tube under its own power, at a very easy initial velocity, just enough to insure accuracy of aim; so the tube does not have to be of heavy construction. The bullet increases in velocity as it goes. It may be solid or explosive. It may explode on contact or on time, or a combination of these two. From Armageddon 2419 A.D. by Philip Francis Nowlan (the original "Buck Rogers" novel) 1928