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I want to be a bit more creative in my design of medieval weapons, and have begun looking into the creation of an Arbalest that instead of shooting traditional crossbow bolts, shoots metallic cylinders. At the moment, I don't have a set size for these aforementioned cylinders, and the material can change too. If those help, please feel free to work outside of what i have had set originally. The intended goal of this weapon is to be a short range, high impact weapon that can hurt someone with plate armor on.

The armor in question would be of a high quality, nondescript steel, lets say 6.6 mm thick (What seems to be the upper echelons of armor thickness for most breastplates generally.)

How could I make my dream weapon, this handheld device that shoots miniature rods of gods into armor wearing foes? Or are my dreams of crushing armor like tin foil with very heavy pringles cans just that? A dream.

The constraints are as follows: Mid 1750s technology, no gunpowder, no magic or any otherworldly force.

If any clarification is needed, my timezone is PST just so I don't keep you up eagerly waiting for my response.

For the armor thickness numbers: http://www.allenantiques.com/Breastplate%20Thickness%20Study.html My original inspiration of this design. https://kenshi.fandom.com/wiki/Spring_Bat

The following are responses to various questions / concerns.

@Kepotx - Yes, it would be in the long run more expensive as a design, though the cost isn't much of a concern to the specific group im tailoring it towards. I also said you can always use a different material if you believe steel to be unsuitable.

@Guran - Its a bit of a complicated setting, one of which isn't entirely of my own design. Gunpowder in all forms and aspects haven't been invented in this alternate 1750, though things like clocks, boats, ballistas, fashion styles, materials and all other inventions are more or less available for my use. Unfortunately it isn't steampunk so I can't just retconn a big ass motor on my project and say "boom, done!"

TLDR: A bit of a tropey technology level where you have boats and architecture and styles of the mid 1700s though with a notable lack of gunpowder in all its forms.

@AlexP: I was thinking the projectile look more like this than a normal arrow. https://i.pinimg.com/originals/27/d6/45/27d645c8c43ae65db85d5872614f58ee.gif Its really just a good ol metal tube.

@Starfish Prime - I apologize, I should have been a bit more clear on what was just me making a jab at my own invention and what was actually serious. I don't have an intention to launch a supersonic steel beam using medieval technology.

Though I do acknowledge the fact that more likely than not, this little design I have constructed is far inferior to crossbow bolts in most, if not all regards, would you believe there be something that could be made (excluding artillery) that would reach near/at the speed required? While proofreading this, the first thing I thought would a beefed up medieval nailgun, however merely by saying those words it already sounds far-fetched.

Once again, thanks for the overwhelming response from everyone, I appreciate it.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monty Wild Mar 7 at 17:18
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Why not? If you want to throw cylinders at people why let common sense stop us?

Stabilization

There are three common methods of stabilizing a projectile so that it can actually hit something. We can ignore making it symmetrical because you have a specific shape in mind. We can also ignore aerodynamics because you specifically wanted a solid cylinder not just a crossbow bolt. That leaves only spin stabilization.

The next question is which way we want it spin. Since it is a cylinder we only have two options. It can rotate around its long axis like rifle bullets do. Or the short axis like throwing axes and knives do.

Both are actually possible but spinning end over end fits better. The necessary velocities are smaller so it is simpler for a mechanism to produce. It also has the added benefit that energy of the spin will likely be added to the impact. And the tumbling cylinder might spin over a shield and hit the person behind it. Rapidly spinning object is simply harder to deflect.

Recoil

Since the energy is proportional to mass and square of velocity and impulse to mass and velocity, a heavy cylinder will have much higher recoil impulse than a lighter projectile of same energy would.

Basically if you want your cylinder to have same recoil as a bolt weighing the tenth of it, you must divide velocity by ten and the energy will be cut by the same factor.

Fortunately you wanted short distance so we can simply drop the velocity and get the impact from the energy stored on the spin instead. The obvious downside is that this does not even sound like a crossbow.

How would it work

First, you prop the monstrosity up on its stand, similar to ones used with muskets in another world, pointed in roughly the right direction and elevation.

Second, you connect the cylinder from its middle point to a holder which connects to a gear box which connects to a hand crank.

Third, you crank the spin up. You probably want to only put in the best speed when it is time to fire. This is a short range weapon so you won't have time for a second shot and should not rush it.

Fourth, disconnect the gear box from the holder and make the final aim.

Fifth, connect the gears on the holder for the now rapidly spinning cylinder to toothed rack rails on the body of the monstrosity. This converts part of the spin energy to forward motion. At the end of the tracks the holder releases the cylinder that keeps going forward towards the target.

Sixth, pray that it hits the target and he doesn't just laugh at you. Although a laughing enemy is much easier to run away from than an angry one.

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  • $\begingroup$ "the impact from the energy stored on the spin instead" how would this impact penetrate plate armor? You may need to turn projectiles into self-drilling screws. $\endgroup$ – Alexander Mar 5 at 17:33
  • $\begingroup$ Would it possible / practical to pre-load this design? Or is that just asking for an accidental discharge of a metal rod in your foot. $\endgroup$ – TryaxReck Mar 5 at 18:05
  • $\begingroup$ @Alexander It rotates the other way. So it penetrates the same way as a mace or, if you add a blade, an axe. In fact your point is the reason I chose this axis of rotation. A thrown drill would be kind of dubious. $\endgroup$ – Ville Niemi Mar 5 at 18:09
  • $\begingroup$ @TryaxReck Pre-load sure, pre-charge not really. The same spin stabilization we want limits your ability to move the weapon once the cylinder spins. Unless you have good ball bearings the energy losses make pre.spinning fairly pointless as well. It should not be that dangerous though since the cylinder is held from its axis of spin. $\endgroup$ – Ville Niemi Mar 5 at 18:13
  • $\begingroup$ "divide velocity by ten and the energy will be cut by the same factor" you've missed a square root in there. $\endgroup$ – Starfish Prime Mar 6 at 20:44
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Could a steel cylinder punch through plate armor?

Yes.

[I] have begun looking into the creation of an Arbalest that instead of shooting traditional crossbow bolts, shoots metallic cylinders

...aaand now the answer is no.

this handheld device that shoots miniature rods of gods into armor wearing foes?

Rods from god are travelling at a few kilometres per second when they hit their target. Similarly, an APFSDS antitank round travels well over a kilometre per second. These things are deadly because they are heavy and because they are very fast.

Or are my dreams of crushing armor like tin foil with very heavy pringles cans just that? A dream.

Firstly, firing a supersonic projectile from a crossbow sounds frankly impossible. I don't even think that with near-magical scifi materials you'd be able to do this.

Secondly, firing a very heavy projectile from a handheld crossbow is likely to be disappointing because there's simply not enough energy stored in the bow to throw that projectile very far, or very fast. It will have a low kinetic energy, and therefore it will be exceedingly non-deadly. A regular crossbow quarrel will outrange it, be far more deadly, be cheaper to produce and you'll be able to carry a whole load of them with you. Your weapon is literally worse in every possible way.

You might be able to do this if you use a very large device, like a ballista. Clearly, artillery weapons will have decent range and striking power, though aiming and firing them isn't going to be as easy or as quick as a handheld device. It will be much less portable, too. If you were using a ballista then you may as well just use regular ballista bolts with a suitable tip... cheaper, lighter, easier to produce than great big chunks of metal.

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  • $\begingroup$ Imagine the recoil on such a crossbow... $\endgroup$ – Plutian Mar 5 at 16:07
  • $\begingroup$ @Plutian more than a normal person could handle, for sure. $\endgroup$ – Morris The Cat Mar 5 at 17:55
  • $\begingroup$ @MorrisTheCat Would you rather be a regular person with a magical weapon? Or a someone magically enhanced so they could use a regular weapon that is oversized and overpowered to the point where it could not be practically handled? Who wins? Regular guy with magic cross bow? Or magically augmented guy carrying a regular ballista around like a pistol? $\endgroup$ – DKNguyen Mar 5 at 23:04
  • $\begingroup$ @DKNguyen I don't understand why any of those are necessary. $\endgroup$ – Morris The Cat Mar 6 at 1:16
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Ok, so let's talk about the actual forces involved here.

Using a rough calculator intended for hydraulic presses, with the 6.6mm armor thickness you mentioned and assuming a 2cm projectile, you'd need 16 TONS of force, which works out to about 160 KiloNewtons.

For comparison, the most powerful hand-held arbalests ever built only managed about 22KN, so you'd need almost eight times as much force as a real historical arbalest.

EDIT: Interestingly, it turns out that the .50 BMG round fired by the very largest sniper rifles and heavy machine guns ALSO generates about 20KN of force, but of course has even better penetration since there again it's smaller and much, much faster than your proposed projectile, and like the real crossbow quarrels is pointed.

The important thing here is that the real arbalests could penetrate that steel plate too, they just did it using a lot of mechanical advantage from the armor-piercing tips. Your rod-from-god requires eight times as much power for no corresponding benefit whatsoever.

As some other people mentioned, recoil is also an issue here. Conservation of Momentum is absolutely a thing, so in order to fire a projectile forward with 160KN of force, you're going to apply that same 160KN to the person firing the weapon.

For comparison, a car travelling at 60m/h hitting a wall applies about 500KN to the wall, so your abalestier would get a third of that. It might be survivable, but he wouldn't be firing a second shot.

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  • $\begingroup$ People have used things like a shoulder-braced 20mm rifle before, the recoil from which would not have been at all fun even if you were thoroughly braced and prepared. An arbalest of the power you require might well have less recoil, as the damn thing would need to be massive and so have a fair amount of inertia. $\endgroup$ – Starfish Prime Mar 6 at 20:48
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Yes, kinda. It should be mentioned that there is already a string propelled rod that pierces plate mail, and it simply needs some ash wood and a bit of metal. Of course, it has to be fired from the English Longbow. History tells us that these bows turned the tide in some early battles by taking out knights.

Now, there are some caveats there. After invented, they started making more advanced plate mail, which it couldn't pierce nearly as well. And of course it is a rod with a pointy bit at the front.

But if you modified the tech some, had a crossbow with incredibly sturdy materials that held a lot of energy (let's say that it has to be wound using a pulley system to transfer all the energy it needs without Hercules arms), and maybe sharpened the edges of the rod/bolt, you might have something there.

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  • $\begingroup$ Your answer ignores the differences between a real arrow/quarrel and the metal rod that the op proposed in his post though. $\endgroup$ – Morris The Cat Mar 5 at 18:40

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