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I'm looking to create a syringe gun for um....reasons.

Don't worry about the specifics, I'm not looking to assassinate anyone (at least not too much), but I want to be the new Vaccination Vigilante®. I plan to have liquids of all sorts be added to this weapon, so microscopic syringes won't do. It needs to at least have enough capacity within the ammunition for me to use the below listed "fillings".

  • Vaccines
  • Bloods with viruses
  • Poisons
  • Toxic chemicals
  • Filtered Apple Juice
  • Paralytics

I also need it to shoot relatively far (400+ meters), remaining stable enough to inject into the incredibly thick skin of.....nevermind. The targets don't matter, assume normal human skin is the target.

How can I create a realistic syringe gun given these "fillings"? Would a tranquilizer gun fulfill these capabilities?

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    $\begingroup$ It sounds like you're just giving a specialized name to a tranquilizer gun. Google "tranquilizer darts" and see if that projectile is really any different from what you're currently imagining. $\endgroup$ – fenix d.Anconia Jan 12 '17 at 18:46
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    $\begingroup$ Doesn't really matter WHAT you put in the tranq-darts; they're designed to inject whatever on impact. $\endgroup$ – Erik Jan 12 '17 at 18:49
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    $\begingroup$ @Erik Actually it does, as viscosity of the liquids could prevent the size of the needle delivering necessary amounts, but the range could pose a problem depending on the density (and likely weight) of them. $\endgroup$ – Anoplexian Jan 12 '17 at 18:53
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    $\begingroup$ Filtered Apple Juice, gasp, you monster. You want to kill me. I'm allergic to apples! $\endgroup$ – M i ech Jan 12 '17 at 22:09
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    $\begingroup$ This is perfectly on-topic...we have a weapons tag after all... $\endgroup$ – James Jan 12 '17 at 22:12
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A tranquilliser gun would fulfil all of those requirements, with the notable exception of range. Getting 400m range would become very tricky, for the following reason:

  • In order to hit a target, you need velocity: velocity gives you a flatter trajectory, less wind-effect and makes lead easier to calculate for a moving target. As the range increases, these things become increasingly more important (as the round will also slow down more the further it flies).

  • A tranquilliser gun however needs - by its very nature - to have a low velocity, as it fires a large projectile and isn't supposed to have any destructive effect.

The only way I can think around those conflicting requirements is to have a guided projectile - essentially a miniature cruise missile. That way, it can fire at a low velocity (and maintain a steady velocity) out to a long range. A small rocket motor, wings and a miniature guidance system would be needed - laser SACLOS or possibly beam-riding would be my suggested guidance system.

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    $\begingroup$ get your range through the use of drones - not exactly as planned, but send a drone equipped with a dart gun at the target, or just have it ram the target. $\endgroup$ – pluckedkiwi Jan 12 '17 at 18:54
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    $\begingroup$ Love the idea of a mini cruise missile. Wouldn't heat-seeking work well for this? $\endgroup$ – Matej Lieskovsky Jan 12 '17 at 19:29
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    $\begingroup$ Heat-seeking might be an option, but against people it would have to be a very advanced system - the advantage of systems such as SACLOS is that most of the tech is carried on the launcher, so that the projectiles can be small and relatively inexpensive. The disadvantage is that they're not fire-and-forget - but with the engagement times for a system such as this at 400m wouldn't be that long, meaning it shouldn't be much of an issue. $\endgroup$ – Matt Bowyer Jan 12 '17 at 20:50
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    $\begingroup$ What about a smart projectile that is fired at a high speed, and deploys a braking mechanism once it is about to hit something? $\endgroup$ – SPavel Jan 12 '17 at 21:59
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    $\begingroup$ It doesn't get exponentially harder. That would mean that, e.g., moving the target 1m farther away would make it twice as hard to hit (or some other factor, such as 10% harder or three times harder). That's not a plausible scenario. For a more mathematical approach, note that all of the forces on the projectile are described by polynomial functions, and the effects of those forces are computed by integrating or differentiating. If you start with polynomials and apply arithmetic operations (+-*/) and integration and differentiation, you end up with ratios of polynomials, not exponentials. $\endgroup$ – David Richerby Jan 12 '17 at 22:03
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Quite simply, you won't.

You have two main problems.

1) Projectile

Bullets are just pieces of metal. They might even be highly engineered pieces of metal (or even ceramics) depending on the round. What a weapon shoots is a round: the combination of casing, propellant (gun powder), bullet, and primer (which ignites the powder).

A syringe gun doesn't have those components, because a "dart" is not a bullet. It is not a "dumb" projectile meant to penetrate, or otherwise injure the target. Therefore its a lot more fragile, it can't take the forces which are exerted on the bullet.

2) Aerodynamics and force

When your dart slams into the target it must achieve 3 things:

  • Be aerodynamically stable and hit the target
  • Deliver its payload into the target's body successfully
  • Not hit the target so hard that it penetrates it (like a bullet does), or so weakly that the payload is not injected

But darts, as we've established, are not bullets. They are not nearly as aerodynamic. And they carry no propellant (not that they could survive the pressure generated by igniting a serious amount of gunpowder), therefore they must be fired using compressed gas.

And so, right off the bat, you have 2 major impediments to shooting a target at 400 meters. Shooting a dart full of liquid 400 meters out would require a heck of a lot of pressure and force. So much, in fact, that the dart probably won't survive, and such a gun would require some serious pressure tanks to operate off of.

Second, darts are fired out of smooth-bore guns, they are not made to be shot out of rifled barrels. This all means that they will be way more aerodynamically unstable than a bullet. Hitting something at 400 meters is essentially a pipe dream (pun intended).

Conclusion

Dart guns are meant to deliver a payload at short to medium ranges, and must typically be well aimed, as the dart should not impact the target in the eye, for example. What you're looking to make is some sort of dart sniper rifle, and that won't work.

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  • $\begingroup$ Well, current darts are fired out of smooth-bore guns at low velocity because that fits our current needs for dart guns, however, dart-like objects certainly can be fired out at high velocity and/or rifled barrels when using appropriate sabots, in a similar manner as various anti-armor rounds (e.g. en.wikipedia.org/wiki/Kinetic_energy_penetrator) work. Also, if you have strict limits of acceleration, then small rocket ammo is possible (e.g. defensetech.org/2015/10/12/…), and they could be made with a syringe tip. $\endgroup$ – Peteris Jan 12 '17 at 20:01
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    $\begingroup$ @peteris - you do realize that the target is supposed to survive, right? $\endgroup$ – AndreiROM Jan 12 '17 at 20:13
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    $\begingroup$ If the rocket doesn't have the explosive payload, and is twice smaller in every dimension and 8 times smaller in weight because it doesn't need to carry an explosive payload, then it could be a painful but nonlethal hit - the rocket can be made quite slow compared to bullets, in essence a tiny single use winged drone with a chemical "jet" engine. But otherwise yes, as you state, any unpowered kinetic projectile that's fast enough to be accurate at 400m is totally deadly - the slower types of gun ammunition e.g. most (all?) pistol rounds are unusable at 400m even when fired from a long barrel. $\endgroup$ – Peteris Jan 12 '17 at 20:22
  • $\begingroup$ @AndreiROM The bullets I use for my personal defense pistols are actually a polycarbonate. $\endgroup$ – Der Kommissar Jan 13 '17 at 0:39
  • $\begingroup$ Interesting. Now I can no longer suspend my disbelief for the Overwatch (video game) character Ana -- who is a sniper who shoots high-speed healing syringes! overwatch.gamepedia.com/Ana $\endgroup$ – HC_ Jan 13 '17 at 19:19
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I have given this matter much thought. One could make a fine syringe arrow. A 10cc syringe would be the tip of the arrow, the shaft of the arrow tipped with the rubber gubbin and acting as the plunger within the syringe. An arrow is stable in flight. 400 m is doable (ok, you might need a footbow). On striking the target the (small gauge) needle would go in to the hub, penetrating clothes and so on. Kinetic energy remaining in the arrow shaft would depress the plunger, expelling syringe contents into the unvaccinated.

The syringe bow would be quiet. The previously unvaccinated would probably be less quiet.

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    $\begingroup$ "I have given this matter much thought" - that's not worrying at all. $\endgroup$ – Whelkaholism Jan 13 '17 at 10:05
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    $\begingroup$ Except an arrow with enough velocity to travel 400m is going to do serious (and almost certainly fatal) injury to the target, whatever head you happen to have on the arrow. $\endgroup$ – Graham Jan 13 '17 at 11:43
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    $\begingroup$ if you have something as large as an arrow, you could add a guidance system and a parachute to decelerate it just before impact. $\endgroup$ – james turner Jan 13 '17 at 16:01
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    $\begingroup$ Loosing the string would depress the plunger immediately no? $\endgroup$ – asawyer Jan 13 '17 at 20:45
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    $\begingroup$ @Graham Probably a construction similar an umbrella that is opened by impact-force could solve the penetration-problem. It'd still be painful, but the distribution of the impact-force would be large enough to make the projectile non-lethal. Just like a bulletproof vest, only that it's attached to the arrow instead of the poor sod you're shooting at. $\endgroup$ – Paul Jan 14 '17 at 0:55
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In order to get the range you desire without increasing velocity so high you put a giant hole in your target, you need smart munitions. You would either need a self-propelled munition (e.g. tiny rocket), or a munition that can decelerate before impact.

A tiny rocket would be complicated and would need to include a guidance system.

An air burst round could be interesting, because if properly constructed it could use a shaped charge to send the liquid into the target as a high-velocity stream (like a jet injector), while ejecting the solid matter back away from the target as low-velocity dust. The xm25 cdte rifle has similar exploding rounds.

A tranquilizer gun with "smart darts" is probably the best solution. The gun would fire the dart at much higher velocity than a standard dart gun, but then the dart itself would deploy a parachute immediately before impact in order to reduce it's velocity to non-lethal energy levels. Honestly, the technical challenge isn't that large. I wonder if that kind of smart dart might be marketable for animals in the real world...

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Others here have pointed out the impracticability of firing a large projectile (the syringe) over large distances at less-than-lethal impact velocities. I particularly like the cruise-missile syringe proposals.

I'm going to go for something different. Don't fire a syringe.

Freeze the payload (the vaccine, the apple juice, etc) before firing into a long (ish), thin, aerodynamic shape. Use a laser rangefinder on the weapon to allow the weapon to determine the correct muzzle velocity for the range to allow the icicle to penetrate the target at the lowest speed to prevent damage but ensure penetration.

Use a low-acceleration method such as compressed air to fire the projectile to ensure it doesn't shatter in the barrel.

The ice projectile will then melt inside the target.

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    $\begingroup$ As demonstrated by Mythbusters, ice bullets are too brittle to be effective. $\endgroup$ – Frostfyre Jan 13 '17 at 13:18
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    $\begingroup$ In the link provided the intent was to kill, and I am assuming they were using standard explosive propellant to fire the bullet. OP asks about less than lethal methods to inject a fluid at range. $\endgroup$ – Skrrp Jan 13 '17 at 15:35
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You could conceivably craft a projectile whose terminal velocity is non-lethal yet still stable in flight, and then a fire control computer could aim dumb payloads at severely parabolic trajectories. It wouldn't be so much a gun as miniature artillery, but I could picture it fitting in a backpack, so still portable...

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I agree that range is the primary consideration. But if you're willing to flex that requirement, say hello to my little friend Joerg Sprave. He also has a how-to video so you can build this contraption yourself! Has a number of advantages and disadvantages over traditional tranquilizers, but the main advantage is that it's more fun this way ;)

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