Dec 312015

A nice video describing the Gyrojet pistol. For those who somehow don’t know, the Gyrojet was a neat idea that just didn’t work out: a rocket pistol. The pistols (and associated carbine) were lightweight structures since they were not subjected to the usual stresses associated with firearms… rather than one high pressure explosion, the Gyrojet rounds were propelled by an internal rocket motor that burned for 0.1 seconds or so.  While that was great for the firearm, it sucked for the bullet itself: muzzle velocity for the pistol version was about ten feet per second. Over the next fifty or so feet the projectile continued to accelerate to something like 1200 feet per second, creating a nicely lethal round. But the initial slow velocity meant that wind would easily blow the thing around… accuracy was a bit of a joke.

I’ve often wondered about modernizing the Gyrojet. Apart from the lame fixed internal magazine the firearm itself is fine, but the projectiles could do with an update. A two-stage motor would seem the way to go… a very fast burning first stage so that the muzzle velocity is stepped up to something meaningful, several hundred feet per second. Additional ballistics work to assure something resembling accuracy. Advanced versions with laser seekers and thrust vectoring.

Even the best modern Gyrojet will almost certainly be an inferior weapon compared to a proper automatic. But it’d make a dandy weapon for the Space Marines… the minimal recoil and low system mass would be useful for guys in space suits. Plus, it’d just be durned cool. And let’s face it, that’s reason enough.

 Posted by at 10:11 pm
  • Cambias

    It would need all kinds of high-tech accuracy enhancements and guidance for the projectile, because nobody would be able to afford to practice with it.

    • Scottlowther

      With modern manufacturing, design improvements and economy of scale, I see no reason why, at least in principle, these rounds couldn’t sell for in the ballpark of high-end standard ammo. Two bucks a round certainly seems doable; while that’d certainly break *my* bank, it’s not true for a lot of folk.

      I’d hate to suggest the flavor-du-jour, 3D printing, but it’s possible that that might play a role here. The aft closure plate with the angled jets was probably a good portion of the cost and a good portion of the trouble, due to the precision needed; *maybe* some advanced manufacturing tech could bang these things out to high precision and low cost. My thought would be glass- or carbon-filled cast resin to reduce cost and mass, with pressed-in nozzles made out of something durable but cheap like steel.

      The original gyrojet rounds were simple drawn steel tubes, hard to improve on that. The propellant grains were simple cylinders with holes down the middle. *That* can be improved upon.

      • allen

        $2/round? I know a guy that’s paying $5 a round for good .50bmg to feed his beast of a sniper rifle. I know people who would pay $2 a round to be the guy who goes WHHHOOSSHHH instead of BANG at the range.

        practice would be easy. have shorter-ranged rockets, built heavier so they can be re-used, you catch them, and return to the factory to be re-engined. it’s not that complicated.

  • Phil

    I also think that the initial batch of ammo had some quality control issues to do with the nozzles that badly affected accuracy. I can’t remember the reference though. The company went bust so they never got a chance to get it right.

    Trouble is of course, however cool it is, for terrestrial applications conventional firearms are more cost effective. That said, I’m sure you could get the cost per round down dramatically as long as you were buying large amounts, but where’s the demand ?

    One last thing, if this is being used in space than there’s no wind effects, so an unguided projectile built to modern tolerances may well be accurate enough.

  • kbob42

    Gyrojet like rounds are used by the military now. It is called a “pin flare” and was developed for use by downed pilots. They are also used for signalling traffic in convoys.

  • Bob

    Read “The Meddler” by Larry Niven.

  • xvdougl

    I’d think a rifle version would be just as cool and solve the accuracy dilemma.

    • Scottlowther

      The carbine was a modest improvement, but the basic problem remained. The motor burned out something like 30-60 feet downrange, accelerating all the way. Muzzle velocity was improved over the pistol, but not by a whole lot, and the performance of the round would be, to first order, *exactly* the same as for the pistol. Normally the longer barrel would mean a faster bullet, but that doesn’t apply hear unless you use a larger round.

      A”rifle” rather than a pistol would permit a bigger missile, which would be handy in a number of ways. Manufacturing would be relatively more precise, the motor could be better, active guidance would be easier. Soon enough you end up with the “Pike” mini-missile.

      • publiusr

        Would a hybrid be possible? Have such a gyrojet be atop a regular cartridge? If not that–an airgun?

  • g