The term Gyrojet refers to a class of firearms invented and manufactured in the 1960s. These guns were noteworthy because they fired gyroscopically stabilized rockets, instead of traditional bullets. The half-inch diameter rocket would exit the gun with a low velocity (and very little sound), and then accelerate to maximum velocity about 70 yards from the gun. They were tested by the US Military, and even sold on the civilian market for a few years. The US Gun Control Act of 1968 reclassified them as Destructive Devices, restricted by means of a tax and a license. A second generation was released in slightly smaller caliber that sidestepped this restriction.
Gyrojet weapons have a somewhat unusual appearance, sometimes being described as "space-age", and being very angular, with lots of porting.
The benefits to the gun are it's light weight, negligible recoil, and significant power at long ranges. On paper they are very accurate and have superior ballistics to conventional guns, especially at longer ranges, but quality control issues that affected accuracy in the field made this claim somewhat dubious. They are also reputed to be quieter than a normal gun (similar to using a silencer) and can be fired under water1.
Drawbacks include the rarity (and cost) of the ammunition, and some issues with reliability. Also, as it has extremely low muzzle velocity when first launched, the rocket is very underpowered at point-blank range. Accuracy reports have been quite mixed, and it appears that manufacturing defects in the ammunition may be the cause of much of the trouble there - presumably a gyroscope and propulsion system small enough to fit into a half inch calibre round is somewhat intolerant of manufacturing flaws.
Game and Story Use
- A Gyrojet could make an interesting assassin's weapon, due to it's silence and long-range accuracy. A gyrojet pistol has significantly greater range than most pistols, allowing for easy concealment of a long range weapon.
- Villains occupying an underwater base might employ gyrojets, as they'd be effective in both water and air. Enemies who infiltrate or attack the base, expecting to face only short-range spear guns, might be in for a big surprise.
- Expect writing the stats for a gyrojet fired under water to be … complicated.
- If the PCs were captured, and held prisoner by henchmen armed with gyrojets, it could make for some interesting situations. If the PCs figured out what weapons were being pointed at them from up close, they could afford to rush the henchmen. If the PCs didn't realize the specifics of the guns, they might be rather surprised when the rocket bounced off a man at point-blank range.
- Would be appropriate in a Spy / Espionage genre game set in the 1960s or 1970s. In fact, a gyrojet gun was featured in one of the James Bond movies.
- It could also be used in a pulp-era science fiction story as a futuristic weapon, as in the original Buck Rogers novel, Armageddon -- 2419 A.D.
- Generally very appropriate for rocketpunk or Raygun Gothic settings.
- Onboard propulsion and course correction could make gyrojet an excellent choice for "smart" rounds - either those with some form of seeker head (perhaps heat seeking bullets or those that home in on the biolelectric field of living organisms) or those that fly on a programmed course (perhaps to curve around an obstacle and hit a target on the other side). Both would require a significant improvement in microelectronics - although the programmed rounds might well be feasible with current tech.
- Imagine a weapon that fires a spread of gyrojet rounds into the air where they then correct into a tight grid formation and accelerate downwards as a single barrage, accurately saturating an area of soft cover…
- For Dune style settings with speed-dependant force-fields a gyrojet round might well have a pre-programmed acceleration pattern to allow it to pass through the shield and then accelerate.
- Theoretically the gyrojet principle could be extended to larger calibre rounds as well giving you guided grenade launcher rounds and similar things (as per the GEP-gun from Deus Ex).