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How would you modify a one-handed projectile weapon (preferably a crossbow) to make it trail a long, light string?

Technology Level: Similar to the mid 1800's, but without the discovery of gunpowder or development of modern firearms.

Physics: I'm trying to keep the basic physics of this world as similar to reality as possible, although "magic" will provide a bit of wiggle room here. I'm okay with it not being hyper-realistic, as long as your average college-educated non-expert wouldn't find it ludicrous.

Some Background Info (why I need this):

In this world, certain supernatural abilities are touch-conductive, meaning that they follow rules similar to electrical circuits. Like in electricity, certain materials are more or less conductive to magic.

One guy has figured out that a good way to use his healing abilities over a distance is to just shoot his accomplice with a sharp non-lethal projectile that trails a superconducting string. (Sure, his friend will probably be a little annoyed at first that he has a bolt in his ass, but probably less annoyed after he realizes his internal bleeding is gone.)

The problem is that I'm struggling a bit to understand how crossbows work, and mainly how bolts differ aerodynamically from arrows. I've found that conventional archers can attach string trackers to their arrows, sacrificing some degree of accuracy. However I'm having trouble finding an analogous setup for a crossbow. Is this because the bolt is so much smaller/shorter range than an arrow?

I think that the ideal weapon would have as many of the following characteristics as possible:

  • It's capable of being shot one-handed after loaded
  • It's as compact as possible so as to draw less attention
  • It needs to be able to hit someone 30 yards away (or double that with some extra propulsion from magic*)
  • The string needs to be detachable in some way so someone yanking on it from the other end can't play tug-of-war with his weapon

I'm also a little concerned about the projectile itself--namely, how to make sure you don't immediately kill the guy you're trying to heal. At first I thought of putting a stopping mechanism** on it to keep it from going all the way in. However, when I started drawing a diagram to include such a feature, I realized it would probably not work from an aerodynamic point of view.

Non-lethal Crossbow Bolt

Instead, could I just make it too short and too light to pierce anything vital? (Hitting someone's eye or even their artery is probably ok.) If not, I guess that's just a risk he's going to have to take!

Thanks for all your help! I have the feeling that the answers are out there somewhere but I'm just missing the vocabulary needed to find them.

*You might wonder why he doesn't just use magic alone to propel his projectile and skip the weapon. As it turns out, this kind of magic is a bit too clumsy and inaccurate to pull this off reliably. It's good at providing strong directional power in certain cases, but the experience would be a bit like trying to shoot an arrow by hitting it with a car.

**What's the word for this?

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    $\begingroup$ Did some research, and the only things I could find on the existence of a crossbow string tracker was on a forum where one hunter was commenting the range for him using one was only 15 yards. $\endgroup$ – Anketam Feb 13 '17 at 2:26
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    $\begingroup$ arrows have to have the right flex to fly straight (archer's paradox), crossbow bolts are the opposite they need to be stiff. You may want to look at something called a line gun, which is used to launch tethers between boats. $\endgroup$ – John Feb 13 '17 at 2:52
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    $\begingroup$ This is a great first post! It's well planned-out, you've given us a lot to work with, your setting is crystal clear, and you even included a fancy drawing. I'm looking forward to seeing more from you on here! $\endgroup$ – Zxyrra Feb 13 '17 at 3:42
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    $\begingroup$ I’ve seen fishing reels on bows. So that’s real enough, if you can manage a light and strong filliment. $\endgroup$ – JDługosz Feb 13 '17 at 3:51
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    $\begingroup$ @Dog A taiser is basically do what you are looking for. They shoot out a couple of lines that latch into a person at a very shallow depth. The barb is small enough that causes minimal blood loss if any as the electric charge usually cauterizes the area anyways. As far as what you would use to shoot, A slingshot may not even be half bad ( I know not as cool as a crossbow) but ultimately you don't want to use something that will shoot with heavy penetration power. So as another comment said, range limit will be a factor. Even taisers max out at 15 feet. $\endgroup$ – ggiaquin16 Feb 13 '17 at 18:04
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You should check out some of the tools used by aborists to launch lines,, some of these definitely seem capable of launching a fair distance. Some links:

Someone using a crossbow, seems to get a large distance, looks like more than 15 yards. https://m.youtube.com/watch?v=qz8jG1p63NA

This guy using a throwbag: https://m.youtube.com/watch?v=7v9f6isVx3E Some people on this: http://www.arboristsite.com/community/threads/best-size-for-throw-weight.33808/ have thrown these about 30 yards nearly straight up ,and I assume this distance would be similar if not greater horizontally , but I don't know about accuracy.

This person using a small slingshot. https://treefool.com/2014/04/07/diy-cheap-throw-line-slingshot-vid/ If you're not averse to using one of these(they are twohanded), but very small.

You could investigate something with an atlatl.

I don't suppose a flying disk or boomerang would work.

To be honest however, I think you'd be best off with a crossbow, readers would already be familiar with it and I think the danger of your main character misplacing a shot and injuring his friend would add tension and this would be exciting. To stop his friend from being hurt, maybe said friend could wear some leather armour/a helmet?

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  • $\begingroup$ This is wonderful! You actually found a crossbow with a line! It even shows how the trailing line goes into a notch so it doesn't get caught on the bowstring! I'd have to put some thought and research into whether the reel could have been made before the 20th century, but this helps answer a lot of the questions I had about how things would have to be placed. And your alternate suggestions are great too. Thank you so much! $\endgroup$ – Dog Feb 13 '17 at 6:31
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    $\begingroup$ No problem, also, I don't know if this is practical but maybe the bolts could be considerably thinned about halfway along the shaft and/or have the second half or so of the shaft at a very slight diagonal so the second part of the bolt would snap and not go in upon impact? This would also need some sort of connection of wrapped wire around each side of the break which would keep the magical connection there. Maybe not worth the extra hassle with the bolt but just another idea. $\endgroup$ – Adam Walker Feb 13 '17 at 8:46
  • $\begingroup$ This seems quite similar rto Lserni's, i hadn't seen it but that's two similar ideas now so might be good $\endgroup$ – Adam Walker Feb 13 '17 at 9:09
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As far as the stringy thing goes, you can have the missile have a hollow in the tail with several yards of fine thread coiled in. This minimizes the drag on the missile as well as the friction on the thread. The thread can then be attached to a ring or carabiner on the crossbow, allowing for easy detachment.

Attaching wires to flying weapons is doable, and if the distance involved is less than a hundred yards, there should be no accuracy problems even with your average crossbow:

<--- to crossbow string
    ==============================================
-------\ |\ |...   coils of thread    | WOODEN   --> to point
        \| \|                         | SHAFT
    ==============================================

You can use a bamboo or cane for the shaft, and coil the wire inside.

The nonpenetrating requirement can also be solved in a way, but requires careful construction.

When the arrow hits, the forces in play are the resistance of the victim's flesh and the kinetic energy of the incoming shaft. The part of the shaft that penetrates has very low speed and exerts a backward force on the incoming shaft.

You want an arrow made up like this

================>><##########>

once the first segment ### has entered the target for about half its length, the backward force is enough to break the arrow at >>< - the left part of the shaft will shatter and splinter, and hopefully it won't inflict too much damage. Or it could drive into the right part which is partly inside the body, enlarging it and making its further penetration impossible:

           -------\
================>> >>#####>
           -------/

You can do this by having a solid left-part of the shaft, and a right part made up of several splinters welded together to the right, and held together all around the left shaft by the equivalent of a breakable elastic band that's just enough to hold under the stress of departure from the crossbow. When it hits, the right part penetrates and slows down, the middle part collapses and acts as a shock absorber, and in so doing it pancakes increasing in width, so that further penetration is avoided.

All this must not split the thread connected to the rightmost conductive head, of course.

One other option, probably simpler, is to have a point made of soft wax, with a needle inside. The wax is shaped aerodynamically, and on impact the blunt body of the arrow doesn't penetrate (it might well leave a nasty bruise), the needle does (up to a controlled depth). The wax point can be quite large and offer aerodynamic penetration to a large "shoe" to ensure lack of penetration:

              |WWWW
=============#|WWWWWWWW
             #|---------->
=============#|WWWWWWWW
              |WWWW
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    $\begingroup$ This is just a fantastically excellent answer. The wax with the embedded needle is a really good idea. I wonder if you could combine your last two ideas to make a sort of syringelike mechanism! Maybe the impact of the back half could drive a barbed needle through an otherwise blunt tip into the victim. Uh, I mean, heal target. $\endgroup$ – Dog Feb 13 '17 at 19:50
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The biggest problem here is the definition of "non-lethal" in an age before proper medicine. Any wound is potentially lethal, maybe not immediately, but in the long term. You're dealing with a magical healing here so there's more flexibility, but you're still doing a lot of damage on the way. The chances are your victory here is pyrrhic and you're going to have to get some hands on healing in short order to deal with that puncture wound.

Then there's the range consideration. Any projectile weapon with intent to puncture is going to have a set of ranges: lethal, possibly non-lethal, and useless. The last thing you want to do is punch a hole clean through him because he's a bit too close.

The gunpowder question: Without gunpowder combatants would still be armoured. This is a problem. To penetrate armour the power on such a device would be lethal to an unarmoured target until close to the normal useless range. Again, get your range and armour balance wrong and you're punching a hole straight through him.

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  • $\begingroup$ This may not have to do with the original question, but your point about armor is excellent. I can't possibly have it both ways--either combatants have to be wearing armor or they have to have access to weapons that make armor obsolete. The best part of this whole thread is that it's making me realize that I should reconsider the technological setting for my story! $\endgroup$ – Dog Feb 13 '17 at 19:44
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In the 1970s or 80s I read an article claiming that until recently crossbows were very inaccurate. This was in a discussion of siege warfare & castle defense. I now doubt that information, since compound xbows have been around for many thousands of years. Currently, xbows are as accurate as pistols at modest (30-40 yard) ranges. Scopes are necessary. There is no, I repeat, no safe way to shoot a xbow at someone. You risk maiming or killing them. As you seem to know, bows are used to hunt both fish and birds with strings attached see, for example Wikipedia Bowfishing. I'd guess the accuracy of such projectiles is miserable at any distance more than a few yards. Increasing muzzle velocity (or whatever it's called for a bolt) should increase distance, but will also reduce accuracy while at the same time making injury more likely. Tasers have maximum range of 35 ft and use compressed gas. Serious injuries are rare...at least, so says the law enforcement agencies that use them. Last idea, have you considered a stream of water? I guess getting a continuous 30 ft stream is unlikely...

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  • $\begingroup$ Thanks! Hmm, so increasing velocity reduces accuracy? I had that totally backwards. $\endgroup$ – Dog Feb 13 '17 at 3:01
  • $\begingroup$ (The stream of water idea is awesome, by the way!) $\endgroup$ – Dog Feb 13 '17 at 3:10
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A crossbow imparts the same momentum no matter what. You cannot pull your punch based on range.

So unless you change these to Nerf style suction cup darts, you have a high risk of punching into / through your target. For a healing bolt, you're going to have to heal the bolt-strike and whatever you intended to heal at the same time.

With a standard bow, you can reduce the force for close-up vs long range shots. And that's a plus. But you still have a high risk here.

You might try to make a thing more like real-world taser systems that use tiny barbs and wires. Those are small enough to be non-lethal.

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Anything functional at long range that can carry a line could actually be lethal. Is it really necessary to actually hit the person or just land it near enough that they can grab it? I wouldn't aim a crossbow at a friend, especially if I am going to have to heal them.

If you want a non-lethal projectile think of something like a yo-yo or a blowgun. However, the range may be much shorter than you would like. However, one should consider whether a healer is really also likely to be a master marksman at long range. Also, if your healer is at an extreme distance from his allies doesn't that make him a prime target in many cases? A shorter range weapon may be appropriate since he would still be able to heal from cover or hiding. However, he would still need to be pretty close.

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