Something I'm working on involving human soldiers in the future- I'm trying to decide whether hand-held rail guns or gyrojet firearms would serve as better weaponry, which advantages/drawbacks one might have that the other would not. Which would have better penetrating power? Require less resources to make? Might there be more ways one could malfunction than the other?
Both are pretty bad choices for an infantry weapon. If for some reason you're choosing between these two, any variant you choose is bound to have an impact on your world to be viable.
Let's start with the gyrojet.
You don't have to worry much about the recoil, and the disadvantage of its projectile gaining maximum speed at 20m is negligible if you don't plan plenty of close quarters combat. However, ammo is expended by millions in small-scale conflicts and by billions in large/protracted wars. Its cost is substantial, nevermind the need to throw out billions of outdated bullets and to produce a billion of gyrojet rockets, just to sleep safe. And as gyrojet ammo is bound to cost much more than a comparable bullet (much worse effects on accuracy from imprecise machining), you'd have to find a problem for this solution. Why would it be better than a simple bullet?
Probably, you're recoil-sensitive (zero or low gravity). Or you have to use larger calibers as a standard issue (14.5 equivalent or higher) because of, probably, abundance of well-protected targets. In other words, if enemy soldiers are that protected by their individual armor, that 5.45-.50 won't cut it because of reasons you'll have to invent (power armor of sorts or outright aliens), but your soldiers for some reasons can't endure the recoil without broken bones (no power armor).
Handheld weapons in which projectiles are accelerated electromagnetically (let's not delve into differences between railguns, coilguns and such) are usually meant to accelerate a very small projectile (~2-3mm). You run into all sorts of problems (power supply, very powerful magnets to accelerate a pellet sufficiently over the course of a quite short barrel, heat sinks as you'll have 2-2.5 times of pellet's kinetic energy dispersed as waste heat, weight), you still get recoil, but you have an outstanding armor piercing capability. It doesn't give you much.
Anti-tank rifles of WWI and WWII were a specialist's weapon, as to knock out a tank you have to know where to aim at. To make a general-issue weapon you have to find yourself a peculiar opponent, the one with a large portion of forces heavily uparmored, but vulnerable to armor penetration in at least half of an individual target surface.
If for some reason you postulate superior accuracy of the railgun (1 MOA at 3-4km, to start, hypersound speeds required), you'd better make sure your individual soldier will be able to discern a target at that range (though most time the range of view will be drastically lower), so equip them with sophisticated detection and targeting equipment. While increasing typical firing distance may bring an interesting battlefield, it will be mostly static, if you don't bring in a really increased speed of an individual soldier.
All in all, individual weapons save lifes of individual soldiers, take other individual soldiers' lifes, but attribute only to 1/4 of all casualties (your battlefield may vary). The lion's share of all losses is inflicted by artillery. If you're planning a proper military action, not just a skirmish, your soldiers' weapons are to be a part of the doctrine, meant to have their own place alongside with artillery, drones, attack planes and helicopters, tanks, APCs and IFVs. If for some reason the traditional bullets are ditched, everything else should've changed too.
For the sake of the narrative I'd personally leave bullets for close-range (as a sidearm) and snipers and went all programmable explosion automatic grenade launchers. No ugly trenches this way, just action.
Neither technology is good enough to replace modern firearms in their current state. But, since this is a future scenario question, let's consider we add a few decades of technology to the underlying systems to see if either could reasonably get there.
Gyrojet's big disadvantages are cost and weight of munitions. Bullet per bullet, they are just not as efficient as normal guns, so to make them king of the battle field, you need to make the bullets cheaper and increase the weapon's kill-shots per bullet. One thing that the industrial revolution has taught us is that the cost of complexity is mostly a one time problem that is eaten by developing your manufacturing process, after that, cost per unit is mostly just materials. If you were building gyrojet rounds by the billions, then you per bullet, they would only be a little more expensive than normal munitions.
That said, gyrojets have one distinct advantage in the future that makes them way better than normal bullets that most people don't consider. A low acceleration. As much as this sounds like a disadvantage, weapons with low accelerations can pack on-board systems without breaking them when they are fired. Modern image recognition means a smart gun can already lock onto a target, but guided bullets could respond to follow a target's change in direction mid-flight, compensate for firing conditions that could not be detected at the moment of launch, home in on soft spots in a target's armor, avoid friendly fire, or even act as a smart swarm whereby a burst of bullets could sort it self so that a 12 round burst could land kill shots on a group of 12 separate targets with no 2 bullets being wasted on the same one. It also means that you can add various specialized payloads to gyrojets including explosive, incendiary, shape charge, and any future other payloads you want to explore.
Coilgun's big disadvantages are the cost and weight of the weapon itself. Miniaturization will be pivotal, but there are more technological obstacles in making future coil guns than future Gyrojets. Coilguns need to manage heat, and the smaller and lighter you make it, the less dissipation surface and sequestering volume you have to do this in; so, even if you do make a reasonably small and powerful weapon, you'd need an added layer of complexity in heat management that may require a little bit of hand waving. They are also much harder to make rapid fire since you need to recharge the capacitors between shots. Also, coil guns aren't just more complex than other guns, they require a lot of rarer and more expensive materials for all those electromagnets and power systems; so, they will always cost more than the alternatives regardless of how much you mass produce them. This added cost is offset to a degree with cheaper munitions.
As for mechanizing coilguns, its higher muzzle velocity makes on-board electronics less possible but also less necessary than on conventional projectiles since the time from launch to impact is so much shorter. By placing all of the electronics on the firearm, you save additional costs by not using disposable electronics systems on the munitions, but you also lose some versatility. A smart gun has to see it's target when you fire, but a smart bullet can be fired through a visual obstruction, then make decisions based on what it sees when it comes out the other side.
Over-all, the gyrojets are probably the better weapon. Higher rate-of-fire, more options for smart systems, more options for payloads, and fewer engineering hurdles add up to not just a better weapon, but a lot of cool plot points for making your future tech feel more "futurish".
One last reason to downvote coilguns is that by the time your tech reaches the ability to miniaturize power systems enough to make them into practical infantry weapons, you will basically have everything you need to make a wide variety of equally portable energy based weapons. An electrolaser has a whole different set of versatility that a coilgun can't compete with. It can be modulated to stun, kill, sweep for mines, EMP a vehicle, etc. So as an infantry weapon, the coilgun will be obsolete by the time it is practical to begin with.
You will have a lot more options for designing near future weaponry, if you don't try to force a decision between these two. Please think about changing the title to something like "Infantry weaponry for a near/distant future setting" if you want to attract great answers. I only looked inside this, because I'm a fan of EM-Weapons :)
What kind of weapon
At this very moment, I can think of three kinds of weapons, that may replace the small firearms used today: electromagnetic waves, electromagnetic accelerated Projectiles and maybe thermobaric guns.
Waves contains laser and maser and... stuff. All kinds of weaponized em-waves. While you will not cut through steel like a hot knife through butter, but you will overheat parts, which will do damage pretty well (especial on "wet" targets like humans, or anything that may act weird when getting hot). With power-storage getting smaller and more powerful, its not unlikely that this will become a big player in future infantry weaponry. In theory a fine weapon, because under combat-circumstances you will hit what you aim for... while you may need to hit it for several seconds. Further, its hard to detect the shooter (but I'm afraid that you might get a path of ionized air if you surpass output-power of 100 Gigawatt; that might be visible).
So... you need energy for these. Lots of. But when this is far future, you might expect weapon-grade diode-lasers, so this stuff could be easy to produce and maintain. Not so far future will back up to gas-pumped lasers, that usually leave some... unhealthy stuff when used. You need to dispose this.
Then Weapons, that accelerate a bullet using magnetic forces. Two possibilities are widely known: Coil (Gaus) Gun and Rail Gun. First one use the magnetic fields created inside a coil (better: dozends of them) to accelerate some metal thingy, second one are two or more metal bars, that get powered with the same current (now I fail to explain this better, because I'm no native english speaker :( ), so the metal thingy will escape using the only way out: forward.
The Rail-Gun does look like its more resistant and more easy to produce, but I do remember that they assume a Coil/Gauss Gun might reach a better muzzle velocity, if they can coordinate these coils in a proper manner.
Point is, you need much electric energy. More than a laser-gun? Good question. And ammunition. That you need to carry around. Count in batteries for power and some kind of ammunition. Oh, have a look at the Mass Effect universe, where they deliver bullets by cutting pieces of metal off a cube right in the gun when pulling the trigger. And thanks to damage effect due to high velocity, you don't need big bullets.
One thing people often do assume is that the projectile needs to be something that do react to magnetic forces. Nope. Well... you can do a magnet force push to everything, if your magnet is powerful enough (even isolators), but they could also sling a snowball (well... no, it would melt)... so they can sling everything that fit into a ferromagnetic sabot. Take this in account. But this has to get reloaded to old way.
Does sound uncommon, doesn't it? No, that not these "spray out gas and enlight it", these things are called... damn... aerosol-bombs? Anyway, its pretty much like a power-projectile, but if I remember right, they don't use explosion / expanding gas, they do use heated / expanded gas. Does sound similar, seems to be much more relaxing for the barrel and may archive more muzzle velocity. And may lack the huge muzzle-flash. But for usage in infantry weapons? I head that this may find its way into artillery-pieces, that cannot afford a ship-size Generator for a rail-gun. Maybe we will see a comeback of the anti-tank gun using this technique, when electric power isn't free available, but a tank with ugly hard- and softkill systems for rockets need to be removed.
To be honest, until now I didn't know there is something like this. Well, I remember stuff like this in the very first Perry Rhodan Story (they brought such stuff to the moon), but I thought it was something the authors used some imaginary stuff. So I'm short of information about this stuff... seriously, rocket-acceleration of bullets? They did this to artillery-shells back in WW2 as a form of range-extending. But these do offer extreme visibility, noise and maybe additional dangers for the own side. And thing about the cost for a single bullet, especially compared to the others. And imagine what happens if your bullet-fuel explode right in your pockets, because of... unexpected heat.
While the time is important, you should specify in what circumstances your weapons of choice should work. Space, low-pressure, common-pressure, hazardous atmospheres (thats a tricky one... High power Laser might detonate gas-constellations that are suspicious to explosion when confronted with a fire, but low-power ones might work), bad weather, dirt and snow and rain, underwater and so on.
Field of usage
You say, that this will be used by infantry-man... but what are they supposed to engage with these weapons? Don't think a Laser or hypervelocity railgun projectile is a super-tankkiller, when the tanks of this area where build to resist such threats.
So.. well, hope this helps a bit.
I'd say I'm partial to the gyrojet, because it is the way cheaper option and would be a better weapon in my opinion to equip to hastily trained conscripts in time of war.
It has alot of basic advantages over conventional firearms, and even gauss guns.
note: I am going to call gauss guns coilguns in an attempt to distinguish them from railguns which could possibly injure the user due to the intense forces required to launch the projectile.
Advantages of a Gyrojet:
- It has very little recoil, at around a tenth of a conventional firearm firing .45ACP since the projectile does all the acceleration, meaning that aim is easier. Whereas a Gauss gun would more likely have slightly more due to the forces of the magnetic field on the gun frame.
- It is extremely quiet making a fwoosh sound similar to the opening of a beverage can, instead of the loud bang of a conventional gun. A coilgun also doesn't make much noise either unless the capacitor discharge required for the high power levels is loud which is more than likely.
- The crack noise of a round going supersonic happens farther away from the muzzle decreasing chance of detection, whereas the coilgun would make an extremely loud crack right at the muzzle.
- The weapon is extremely light, with the average gyrojet pistol massing around 0.4kg since the gun itself does not need to withstand much of the pressure of the propellant, and can be made of light inexpensive alloys or even plastics. This means cheap manufacture and high portability unlike coilguns that require heavy batteries and coils and complex switching hardware.
- Gyrojets also appear very non-threatening so a target unfamiliar with them could easily mistake them for a toy and underestimate your capability. Wheareas coilguns have a huge intimidation factor and would be confiscated in an instant.
- Gyrojets have few moving parts and no need for extraction, ejection, or reciprocating bolt mechanisms which allow high fire rates, and ease of cleaning, repair, and manufacture. They can also be quickly produced in mass numbers from cheap stamped or die cast parts. Rifling is also not required. Whereas the coilguns require a delay between shots to charge up the capacitors, and while they do have few moving parts they require large amounts of electrical engineering knowlege to repair and maintain.
- The rocket propellant is generally clean burning, meaning that hundreds of rounds can be fired with minimal cleaning required afterwards, and overheating is not much of an issue as the rocket accelerates quickly outside of the barrel, and the rocket exhaust vents most of the heat away with it. In comparison, coilguns have no mechanical wear, but the batteries, electrical components, and capacitors would have limited charge and discharge cycles and would wear out over time. They would also be very sensitive to things such as water damage, emp, and the like.
- The flame of the rocket exhaust is only visible from behind, unless you have special infrared optics or the air is really humid and a condensation trail is left behind. However, while the coilgun may not have a muzzle flash the coil discharge would generate lots of heat also visible with infrared optics, and would require a complex cooling system to prevent melting of internal electronics. The exhaust of the gyrojet while still within the barrel, also isn't very damaging and is descrbed by users to be a warm wind.
- The gyrojet gun is operable in almost any medium including space, air, or water. Wheareas a coilgun would need complex waterproofing to work underwater.
- If the gyrojet rocket hits the target before it's propellant is spent, the 5000 degrees farenheit temperature the propellant reaches after it leaves the barrel could ignite or burn the target. The coilgun requires special ammo to achieve an incendiary effect.
- The gyrojet also doesn't start losing velocity the instant it leaves the muzzle like coilguns and conventional firearms, the propellant will provide continous acceleration for a good portion of the projectile flight providing good ballistics.
- The gyrojet gun also requires no internal lubrication since the moving parts are few and under little stress which would be important in environments like space where conventional lubricants would boil off. Coilguns also do not require lubricants, however the complex hassle of maintaining the complicated electronics negates whatever time is saved by not having to lubricate the gun.
- Gyrojets are extremely tolerant of gunk and dirt amd are very, very, very hard to jam and will still fire immersed in water, covered in mud, or contaminated with debris. The rocket exhaust will also blow the majority of the contaminants out of the gun's barrel. A coilgun on the other hand requires meticulous cleaning of sensitive electronics, and dirt within the internals could interfere with whatever sensors are being used to activate the switching between coils.
Disadvantages of a Gyrojet:
The rounds are in general much bigger and heavier than those of normal firearms, which would slightly limit your magazine capacity due to the need to store proellant in the bullet, but they pack a bigger punch overall. However in a coilgun the rounds can be much smaller than those of a normal firearm, however that advantage is offset by the need to carry a massive power storage system including both batteries and capacitors.
The ammunition of a gyrojet is generally more expensive than a normal bullet since the ammo is made of precision components to withstand the pressures and precise nozzle alignment is required for spin stabilization. However, this cost can eventually decrease once the rounds enter bulk production and newer manufacturing techniques are used. Also, once more energetic propellants are developed the rounds can be smaller with even higher velocity. The ammunition for coilguns is dirt cheap since it is simply metal slugs, however that advantage is again offset by the maintenance cost of the complex electronics and the periodical replacement of the batteries and capacitors.
The propellant used in the original gyrojets was slow burning and didn't get up to speed until it reached 9m meaning that at within that window of really close range it would have the poor stopping power of a .22lr, but then would accelerate to have performance dwarfing most conventional bullets. This issue however could be fixed with explosive rounds, or simply faster burning propellants. The coilguns have great performance at all ranges, but for the power they put out, they are simply too bulky, nowadays handheld coilguns made by hobyists are only powerful enough for small game, yet are very bulky.
The gyrojets also suffered from poor accuracy, but according to research which has come to light it was mostly from the poor quality control of the firm that designed them. And in the future the gyrojets could be used as smart bullets. Coilguns have some of the best accuracy of any projectile weapon, this is the only category where they hold clear advantage.
In Conclusion, while coilguns do offer great performance, they have few clear advantages over gyrojets, and most of the issues with gyrojets have simple fixes, but they havent been implemented because, gyrojets have gained a bad reputation due to the shoddy build quality used to construct them and currently there is no market for them. Currently, reliable handheld coilguns that even match the performance of a firearm without unnecessary bulk are currently out of reach with todays technology due to issues with switching between coils and lack of good enough power storage. I strongly recommend gyrojets as the weapons for your book.
For more information on gyrojets and their operation there is alot listed here: