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 Post subject: Gyrojet - any way to improve it.

Posted: 2012-01-20 08:43pm 

Back during the Vietnam War era, the Gyrojet family of firearms was developed, in which it is known for its method of gyroscopically stabilizing its projectiles. Rather than inert bullets, Gyrojets bullets are miniature rockets, which when fired have little recoil and do not require a heavy barrel to resist the pressure of the combustion gases.

Theoretically such a weapon should be great - the Gyrojet had a very light, simple design and its rocket principle meant that it had no recoil and produced an almost flat trajectory. It could also very, very quiet, good for stealth.

Unfortunately, it had a number of problems: When a conventional bullet leaves a conventional pistol it's already travelling at its maximum velocity. A Gyrojet bullet, on the other hand, is still building speed, which causes accuracy problems. The weapon was slow to reload and unreliable, as the rocket shells had a tendency to refuse to leave the barrel, where they would merely hiss away ineffectually. Worse, the ammunition was very susceptible to humidity and fouling.

Thus, the gyrojet never became popular. So here's the challenge - can anyone here find ways to resolve the stated problems and make this weaponry practical again?

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-20 10:44pm 

First of all, what exactly is wrong with ordinary "I blow my load all at once" bullets? That is the question you must ask when talking about unconventional weapons like gyrojet.

Having no recoil is great, but the simple fact is that you cannot have a "rocket bullet" without having very low muzzle velocity. Rocket powered bullets are supposed to do 99% of their accelerating outside of the gun's chamber, but the faster it burns its fuel and accelerates the more of its acceleration it will do inside the gun. As you increase the burn times and thus the acceleration, eventually you get a bullet that does all its accelerating inside the chamber and thus recoils directly into the shooter's body-- in other words, you eventually get a completely conventional gun again. Oh, and you lose the silence factor as well, obviously.

Speaking of the silence, they were quiet, but not completely so. They still had the break the sound barrier, so they ended up creating a sonic boom downrange. I suppose that could still be useful, but for what?

Really, the problem with gyroget was not that it didn't work-- at least, the rifles worked, because they were expected to work at a greater range than the pistols and therefore had all that distance to properly accelerate. There is no reason to ever waste time with pistol-range rocket bullets, because over those distances its simply silly to do your accelerating anywhere but in the chamber of the gun.

Also, you forgot one critical problem with gyrojet. The ammunition was expensive. How to keep manufacturing costs down is one of those questions I doubt anyone here is qualified to answer (I could be wrong), but that brings us back to the question "why?"




Now, if I had to answer that question myself, the only things I can think of are long distance shooting situations where silence is helpful and follow on shots may be necessary. I'm thinking sniping and anti-material rifles, and possibly hunting rifles. Again, don't waste time with gyrojet pistols ever, its amazingly stupid for that application.

Edit: also, see this website http://www.deathwind.com/project.htm

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-20 11:03pm 

I 'm not so sure silence is all that helpful in sniping situations either, at least not at long ranges. By the time the sound of the shot arrives the bullet has long done its duty, and with only the gunshot sound to work on I don't think you can do any better than 'I think the shot came from somewhere thataways'. At best.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-20 11:19pm 

SM93, what do you see as the main advantages of these rounds that make them worth the added cost over a normal round. What do you see them being used for?

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-20 11:41pm 

Why do they have to be supersonic rounds ?
A quick google search shows that subsonic bullets already exist. Including one wikipedia page saying that "Accuracy is reportedly improved with subsonic rounds" because a supersonic bullet can have stability problems as it drops below the speed of sound.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 03:43am 

The problems with subsonic rounds are delay, projectile drop, and damage potential.

The basic problem is delay: the bullet takes longer to get there. A lot longer- which for sniping and antimateriel work can matter, because giving the target three seconds to move before the bullet arrives means you miss more often than if they have 1.5 seconds.

Because of delay, you get projectile drop. At a range of, say, 600 meters, a subsonic bullet will have dropped about twenty meters away from the line defined by the direction the muzzle was pointed. At 900 meters, forty-five meters dropped, and it just keeps getting worse. This makes aiming impractical at long range, and makes the weapon nearly useless for sniping.

Then you have damage. A subsonic bullet carries much less kinetic energy than a supersonic bullet of equal mass. Its armor penetration characteristics will be greatly inferior. To compensate you can use bigger rounds... but to get the same kinetic energy with a bullet that travels at about 1/3 to 1/4 the speed (comparing "subsonic" to high velocity rounds like .50 BMG), you need a bullet about ten times more massive. Which means increased recoil, heavier guns, and bulkier ammunition. Not good.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 04:26am 

One possible future/sci-fi use for them that has occurred to me is as ammunition in some futuristic "gauss rifle" magnetic coilgun. One problem with making handheld weapons more powerful is recoil; a gun that breaks your shoulder & knocks you over is of limited use. With a coilgun/gyrojet combination, the "rifle" could fire the gyrojet bullet as fast or faster than a modern bullet, with as much velocity as the human user can handle (which eliminates the "no power at short range" problem with gyrojets); and once launched the gyrojet will continue to accelerate, reaching a velocity that would result in an impractical amount of recoil if you tried to impart it inside the gun.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 06:03am 

Why not just use a smaller caliber bullet? Impact energies will scale with the square of the muzzle velocity, while recoil scales linearly; the obvious way to take a hypervelocity weapon and make it something shoulder-fired is to use smaller, lighter bullets.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 06:54am 

Still; once they leave the barrel they'll start losing velocity, while the Gyrojet will be gaining it. And I'd think a smaller bullet would lose velocity faster, due to having greater surface area compared to its mass?

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 08:24am 

That is correct. Also, a bullet with a smaller mass would for the same amount of kinetic energy have less momentum than a heavier bullet fired slower. And as far as I understand its the momentum that makes those neat soft tissue wounds and helps penetrate armor.

Furthermore full power rifles are already as accurate and as powerful as is practically required. Give it a little more velocity like you suggested and you already have a bullet that can fly and kill over sniper ranges. The only time your rocket propelled range extension would make sense is if you expected engagement ranges to be something like multiple kilometers. And at that point I don't think your optics would be able to do the job.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 08:27am 

Another advantage that gyrojet rounds would have for a small-arms coilgun is that, thanks to their angled exhaust vents, they would have spin stability. Since a coilgun probably couldn't spin its projectiles, they would otherwise have to have fins for stabilization and sabots to hold them securely in the barrel, like an APFSDS anti-tank round. Finned projectiles would only be stable if fired in an atmosphere, but gyrojet rounds could potentially fly just as straight in a vacuum.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 08:52am 

Well, they are now. I presume that no one would bother creating exotic new guns unless someone else developed something demanding such guns, like better body armor that needs better guns to penetrate it.


I wasn't thinking so much of a longer range as I was thinking more in terms of something that would hit just as hard or harder at long range as it does close up, instead of slowing with distance. Again, I was assuming that if someone developed a more powerful gun it's because they need it, so you'd want that superior impact velocity at range too.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 10:43am 

That's the thing. At actual engagement ranges of modern warfare (400m or so) a gyrojet round won't give you any advantage as what ever speed it did pick up by that time would be negligible compared to what it got out of the barrel. And with any non SMG or 5.56 round the loss of energy over such a range is not that significant.


The question being just what is going to be that tough? Unless we are talking about SF powered armor here there is a very real limit on how much armor a human being can put on before he or she becomes too encumbered to fight.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 04:41pm 

For subsonic rounds, it seems a gyrojet would be a better choice than a bullet. Delay will be less, as the gyrojet could stay near the speed of sound for longer. Shorter flight time means less drop, and faster speed at the point of impact means more damage from the same mass of projectile. And they can have a lighter gun anyway.

Those advantages over bullets would also carry over to supersonic rounds.

Though is it enough of an an advantage to be worth the extra cost of making gyrojet munitions ?
Probably not. If they looked like they could be worth it, then I'd expect someone to be making them in sufficient quantities that we would have real world data about how well they work in comparison to modern firearms.


Apart from 40k bolters, do gyrojet weapons show up in any sci-fi ?

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 06:03pm 

If you're artificially limiting the terminal velocity of the round to subsonic, then the rocket acceleration of the rounds will be likewise limited. Your motor is just a weak sustainer rocket, which makes it even less worthwhile than if it were a powerful rocket, because the gain in energy and speed is less.

See, the problem is that you're saying "subsonic rounds are good, and here's how Gyrojet improves a subsonic weapon," rather than working the other way round and saying "what are the problems with subsonic munitions, is it worth the effort of building them at all, let alone improving on them?"

That gets extremely complicated- and the point of the exercise is to increase energy while holding momentum constant, not the other way round.

For example, Napoleonic muskets were around .75 caliber. The improved blackpowder rifles of the late 19th century trended down toward .45 to .50 caliber; modern rifles fall into the .22 to .30 caliber range. What's been changing, by and large, is the muzzle velocity- big slow bullets replaced by smaller faster ones, which means you can carry more ammunition.

...Why on Earth would you need spin stabilization in a vacuum? There's nothing to make the rounds tumble.

The problem is that as long as you're committed to keeping the bullet subsonic, you can't make it all that fast or powerful for a given caliber. You just can't- Isaac Newton is working against you.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 06:52pm 

When talking about subsonic gyrojet rounds, I was only comparing them to subsonic bullets.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 06:55pm 

So taking already limited use rounds and making them expensive limited use rounds. I think this is why nobody has bothered.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 07:45pm 

It's actually worse for spin stabilization in a vacuum. Due to the distribution of mass around the axis of rotation, a regular round guaranteed to tumble in vacuum. For subsonic rounds, yeah, drop is a huge problem, but adding a gyrojet sustainer won't help much. The rounds are usually so heavy ( a .300 BLK subsonic round is 220 grains, or .5 oz, compared to the supersonic loading of 125 grain), that they don't lose much velocity over their effective range.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 08:01pm 

Sure; Niven had them a few times. I recall in The Meddler a thug expressing shock at the price of the ammo.

"Well, I don't shoot many people."

"At those prices, I wouldn't think so."


Well, the military is working on developing powered armor right now. And armor materials do seem to be improving.

*I* didn't say anything about subsonic rounds.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 08:40pm 

There's an old TSR roleplaying game, Star Frontiers, that used gyrojet pistols and rifles fairly often. There was also the movie Runaway, with Tom Selleck. The villain, played by Gene Simmons, used a gyrojet pistol whose ammunition was fitted with microchips. The gun would scan the target, encode the target's info onto the chip, and when it was fired, the round would seek its target, flying around corners and through obstacles. I seem to remember it having an explosive head, as well.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 09:29pm 

We do have some data, from the army testing of the gyrojet, from the 7 or 8 men who brought their privately-owned gyrojets to Vietnam, and from hobbyists who still manufacture and fire the things.

The relative advantages of the gyrojet are:

-The flat trajectory gives it better accuracy at long ranges.

-The cheap manufacture. Paradoxical as it sounds, a gyrojet gun is remarkably cheap to manufacture. It has fewer moving parts than conventional firearms, and is subject to almost none of the same stresses. You can make the things entirely out of cheap plastic if you want, and it will change nothing except your ability to use the gun as a club. Now, gyrojet bullets are about $100 a round.

The main reason they were never built or issued in quanity is that the guns broke or fouled too easily, and were basically non-functional in very humid or dusty conditions. Though I'm sure the hight cost of ammunition had an impact as well. Frankly, the advantages of greater range and accuracy (They were theorized to outrange contempary rifles by about 20%, the reality is somewhat less but still an improvement) were simply never considered good enough to justify the considerable research costs involved in overcoming the issues.

Plus, then in Vietnam, and now in the MidEast, there really isn't a lot of demand for guns that are virtually useless at short ranges. Or in jungle/desert conditions.

Also, IIRC there was also an issue wherein the manufacturers goofed and 100 rounds were used in a demonstration firing that had 1 of 3 jet nozzles closed and literally could not hit anything the gun was pointed at. The problem was discovered after the demonstration, but unimpressed generals were not at all mollified to learn it was so easy to screw up and issue worthless ammo, instead of the gun itself being insanely inaccurate.

If you wanted to make this thing remotely economical, try thinking of a setting where none of these factors come into play. Like some alien Great Plains-world without jungles or deserts or much concealment or cover, where whoever has the longest-ranged most accurate rifle wins. It's that simple.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-21 09:36pm 

BattleTech originally had them, though they seem to have disappeared pretty quickly (as of right now, the only instance of BT using gyrojet weapons that immediately comes to mind is the original MW computer game) and I'm not sure the Runaway projectiles are quite what 'gyrojet' rounds is about, given that for all practical purposes those were miniature homing missiles.

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-22 03:15am 

BattleTech still has them--there is even rules in the latest rules edition for creating entirely gyrojet armed squads (but then, you can literally arm your squads with samurai swords with elephant rifles as back-up under those rules, so they're hardly a major thing)

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-30 09:56am 

I know a guy with a gyrojet, it's not that accurate as I recall and a bunch of other issues that I can't remember ATM, he got it because he likes collecting strange stuff:



Edit, ah here's the review:
http://www.youtube.com/watch?v=e23o0NIHtFw

 Post subject: Re: Gyrojet - any way to improve it.

Posted: 2012-01-31 01:53am 

Also wouldn't it be easier to just move up the calibre.