How good can you make a crossbow?

Late medieval Europe made some very powerful crossbows, but they were difficult to reload, firing twice a minute at best.

The Chinese made repeating crossbows, but they were not powerful and relied on poison to kill.

Given our much greater understanding of engineering and physics, was it possible to make powerful crossbows that fired at a higher rate with the material constraints of medieval technology, or was what the people of the time made, the best that could have been done?
 
Crossbows can store a pretty significant amount of force, far more than what a human can draw themselves. That has always been the biggest limitation on crossbows. Humans aren't that strong, but we are smart and long ago we realized how to gain mechanical advantage in order to do more work. For crossbows, that was usually a winch. A crossbow winch allowed far greater draw weights to be used since more force could be applied, but like all forms of mechanical advantage, it has a drawback. Winches can only be turned so fast, and that limits how quickly you can fire a high draw weight crossbow.

The modern solution in bows is to use pulleys as seen in the compound bow, but it can just as easily be applied to a crossbow. That allows a huge mechanical advantage, allowing high draw weights, while being fairly quick to draw. Compound bows weren't invented until 1966, but there isn't anything technologically stopping them from being made before then; pulleys are ancient.
 
Crossbows are actually an ancient weapon. The Inuit had a version of the crossbow and giant crossbows were used as siege weapons. You had the ballista and it's descendants,there was the harpax and there might've been a repeating version known as the polybolos. I wouldn't rule out poison as that can be a powerful weapon in itself. Maybe flaming bolts from either a standard size crossbow or a ballista? Leonardo DaVinci had plans for a rapid fire crossbow and compound crossbows would be impressive. I know wrist mounted crossbows are popular in fantasy fiction,but have no idea how viable they are for the ancient/medieval time period. But it seems that crossbows in themselves are very versatile weapons with few limits.
 
And it seems that in World War 1,the French used a bomb throwing crossbow called the Sauterelle while the British had a counterpart named Leach trench catapult that was a crossbow/slingshot combination,so crossbows could get very powerful indeed.
 
Looks like the big problem with making a medieval compound crossbow would be finding a bowstring that's thin enough to go over the pulleys but doesn't stretch hopelessly, particularly in wet weather. Some medieval crossbows were strung with metal wire, but that would likely be too stiff for a compound.
 
@Timmy811

I am sorry I didn't react to this discussion earlier, though I was meaning to. It's a good discussion, though one where there is a lot of ground to cover, and from multiple possible angles.

Compound bows designed and manufactured prior to the 20th century are a pipe dream. You could theoretically invent them in the 19th century, but they'd be more cumbersome and have potential issues with the cables acting as bowstrings. Compound bows being invented in OTL was a bit of a fluke, and fully relied on materials science advances and industrial manufacturing advances made in the 150-200 years prior, during the various stages of the industrial revolution. You might as well ask why 15th century people didn't figure out Henry rifles. The tech, materials and necessary economics just weren't there yet. This is also why revolvers were invented in the 16th century, but only became viable for mass production some three centuries later.

You can get good spring steel crossbow laths (bows), but even those from the OTL early modern era were already reaching the upper limits of their effectiveness as an integral part of military shooting weapons. Like a good barrel is integral to a gun, so too is a good lath integral to later types of European crossbows. With improvements to steel manufacturing in the industrial era, providing improved steel quality, you could raise the potential performance of a steel crossbow lath a bit more. Even without any further mechanical tinkering. Some of the high-poundage laths used already in the 15th and 16th century were powerful enough to shoot a bolt through someone, or pierce through most lighter types of armour, with the major exception of plate armour. (Part of its popularity. Even the high-quality crossbows of the time were incapable of piercing it, though they could dent it or knock you off your feet on impact.) I don't think you can vastly improve crossbow laths all that much, even with 18th and 19th century technological improvements

Bear in mind, the crossbow was still under further enthusiastic development even long past its military prime. People were still coming up with new ideas for hunting crossbows, recreational crossbows, etc., etc. Some even had the earliest variations on what we'd call "tacticool" accessories. Flip-up metal sights, bolt-clips (bolt-holders), late examples had made the trigger mechanism even more complex, going beyond even the rolling nut and lever system improvements that were last done in the Renaissance, the last time crossbows still saw wider military use.

One development related to spanning the bowstring, potentially speeding up things by not necessitating separate spanning tools, would be integrated spanning levers. These occured in the early modern era. They seemed to have been invented at the very tail end of the Middle Ages, even Leonardo da Vinci apparently designed one such specimen. His Italian example was referred to as a balestra veloce, "fast crossbow", and the Germans apparently knew about these ideas too, since a near-identical design appeared in the early 16th century Codex Löffelholz. These crossbows aren't vastly different from other 15th and 16th century crossbows with the traditional nut mechanism and a steel lath, but they are mechanically more complex, because of the integrated spanning lever and the sliding rail parts and steel pivots it necessitates. The fact that these never became a common design seems to be largely down to the obvious extra construction expenses and the extra complexity.

I think an even better design for an integrated spanning lever occured with some other, smaller 16th century crossbow examples, and you later see it crop up a fair bit among small recreational and hunting crossbows in the 17th to 19th century. In that first case, you have the "latch", a latchet crossbow, which was popular in 1500s and early 1600s Britain whenever you needed something that could be reloaded faster than a pistol or petronel or carbine, and could be used similarly to these guns on horseback, even shot with one hand. The integrated spanning lever moved upward in this design. Part of the top-mounted trigger was linked to it and you couldn't really shoot until the lever was collapsed back into the stock and secured by a safety. The thing was quick to load, and though it was aweaker crossbow shooting shorter bolts, it was more than adequate for small-scale ranged combat. Then you have the closely related Balester, Kugelbogen, etc. small bullet-shooting crossbows (pelletbows) of the 17th to 19th century, which used more or less the same top-mounted spanning lever and top-mounted trigger design as the latch. Oddly enough, though a lot of these early modern pelletbows were for recreation and fun only, some were also used for hunting small prey. Birds, hares, that sort of thing. A slightly weaker, less serious small hunting crossbow. So, that about covers both of the two main OTL historical variations on spanning levers directly integrated into the bodies of crossbows.

In a world where no one ever invented gunpowder - dubious, as even in OTL, medieval Europe knew about gunpowder by the 13th-14th century and was making its own guns by the 14th and 15th - crossbows would probably remain some of the most powerful ranged weapons. Some of the minor innovations we saw in OTL would probably occur even in such a world. Flip-up sights, bolt-holders, further refinements of the triggers, integrated spanning levers, whatever would be possible. In the case of crossbows with a design like the latchet crossbow, I think it could grow in popularity as a sort of rider pistol or carbine equivalent, though it would never be an all too powerful crossbow. But still easier to span, reload and shoot quickly and easily from horseback (even one-handed) then other, full-sized early modern horseback crossbows (which often required the use of a cranequin winch, slowing down fast reloading considerably). In a no-guns world, these smaller crossbows would be practical for self-defence and patrol or law enforcement use, as well as for banditry. (Aside from law enforcement, they were used for all that in OTL history as well.) Most of the improved infantry crossbows in a no-guns world would be generally similar to the most refined 17th-19th century civilian crossbows, especially the ones used for hunting. I'm puzzled how some of these features would be used militarily, I suppose acessories like flip-up sights might be eschewed in such contexts, while other innovations might be kept (especially the trigger mechanism advances).

If an industrial revolution occurs and you get similar enough tech developments for the next several centuries, you could eventually see some vaguely steampunk-ish looking crossbow being used by those who have a use for them. As you correctly mention, the historical examples of repeating crossbows were underpowered, and additionally, their gravity-fed magazines made them awkward to aim. Unless an industrial revolution era invents an idea for a light-enough crossbow magazine that's spring-loaded and not in the way, and doesn't compromise the performance of the lath, you could maybe see occassional multiple-shot crossbows. I doubt they could carry much bolts in one go, though. I have pondered about a revolver cylinder like bolt magazine, but the more I ponder it, the less plausible it seems to me on a mechanical level. It would be far more cumbersome than a revolver cylinder that only needs to carry bullets (+ powder) or cartridges.

Another major question: Aside from the above example of an ASB/fantastical world without gunpowder, what would the military role and advantages of crossbows be in a world where guns have already become the mainstay of standing armies ?

As I mention above, crossbows did indeed keep getting better and more technologically intricate even after their final big hurrah in the militaries of the Renaissance, but what would they be used afterward ? If it's cheaper to manufacture musket balls from stone or lead, and only somewhat pricier to manufacture an arquebus or a musket or an early rifle, and then fairly cheap to train a gunner, what role would military crossbowmen play ? You'd be hard-pressed to figure out a decent major role for them on the battlefield or in sieges. I think if you had some adequate reason for crossbows surviving in common military use for longer, they'd be still niche, specialised weapons. Sort of similar to the role they've assumed in the contemporary world, especially the modern models, built with modern tech advances. In law enforcement and some militaries, they're used for counter-terrorism (where guns could set off bombs, or when stealth is necessary), for shooting grappling hooks and scaling walls, and a number of niche roles. But even that is fairly niche.

In a world where crossbows are not entirely kaput militarily by the 18th century and later, I could see them being used by ambush, skirmisher and scout units of soldiers. Irregular infantry, basically, sort of like chasseurs, jägers, pandurs, etc., etc. They would use them for stealthy kills and stealthy attacks. However, even with this, I can see a clear snag. By the second half of the 18th century, research into airguns had really advanced. Funnily enough, the Habsburg monarchy kind of led these developments for a while, with Mr. Girardoni's famous repeating "air-lock" rifle. A Henry-style tube magazine that could hold 20+ leaden rifle bullets, an air cylinder in the stock that needed regular recharging with the pump, but could last until all bullets were shot, and then some. The Austrians used the rifle from the reign of Joseph II to their participation in the Napoleonic Wars. Since only a few thousand were made and remained a semi-experimental rifle (sort of the Steyr AUG of its day), they performed a niche role among the Austrian irregular infantry, particularly the sharpshooters. Napoleon apparently despised airgun sharpshooters, including Austrian ones, considering them "dishonest and sneaky". I reckon the Austrians considered themselves merely stealthy. The ultimate point, though, is that if you have a world where there's no gunpowder, but airguns like this can be invented, why would you give crossbows to irregular infantry ? And if the world has gunpowder guns and airguns, why would irregular infantry bother with crossbows altogether ? They could get the same sort of needed performance and stealthiness out of the aforementioned air rifles. About the only irreplaceable tactical use for crossbow in the militaries of a pre-1900s but post-Barocque world would be launching grappling hooks in sieges and for boarding actions, or secrely delivering small messages on pieces of paper wrapped around a bolt. If an airgun can stealthily take out or assassinate someone, you don't need to bother with a crossbow for the same sort of tactical military use, whether with Napoleonic era sharpshooters or other types of soldiers.

And when Lewis and Clark set off for their expedition, they bought one or two and had them shipped from overseas, in order to avoid running out of gunpowder far from European settled areas. A fine idea. But therein lies the rub: If crossbows would be preferrable for the same job, even in a world of flintlocks and the first successful airguns, why would they have picked an airgun over a crossbow ? Crossbows weren't unknown in North America even at that time, they could have taken a hunting crossbow instead. But I suppose that as with military and other civilian guns, the ammo argument won out. Crossbow bolts are more complex than musket balls and rifle bullets, period. The Girandoni rifle kit didn't include swappable air tanks and the pump alone, it even had a ladle for making your own lead bullets even in field conditions, in the wilderness. For a crossbow bolt (especially of those times, before lightweight modern materials), you need a wooden shaft, you need rigid or feather fletching for the two necessary flights at the back, and you need an adequate type of steel arrowhead (the more multipurpose and less specialised it is, the better in a long-term wilderness expedition). Additionally, most people by then were familiar with long gun use, fewer used crossbows even for hunting. So it's no wonder they chose a somewhat quirky, semi-experimental air rifle over a crossbow. They knew rifles, they knew leaden bullets, they wanted one that could work without gunpowder, and didn't want to fiddle with laths, bowstrings, bolts and other finicky crossbow necessities. The Girandoni could shoot some 20+ bullets in a row from its tube magazine. Even the best possible hunting crossbow they could buy in North America or Europe would be a single-shot. Ergo, it's no wonder they went with a non-gunpowder gun over a crossbow.

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Some good videos on the subject (mostly by Leo Todeschini, since he's a real expert on the whole subject and has made many faithful crossbow replicas):
Hopefully that answers plenty of questions.

In the past, we have had several discussions about crossbow developments and the status of crossbows in a world without gunpowder weapons. You can find them here and here, on our wiki.
 
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Looks like the big problem with making a medieval compound crossbow would be finding a bowstring that's thin enough to go over the pulleys but doesn't stretch hopelessly, particularly in wet weather. Some medieval crossbows were strung with metal wire, but that would likely be too stiff for a compound.

Compound bows designed and manufactured prior to the 20th century are a pipe dream. You could theoretically invent them in the 19th century, but they'd be more cumbersome and have potential issues with the cables acting as bowstrings.
grooved Cams and pulleys are doable in Bronze, and braded Silk cord for cable.

but the problem remains for fast recocking of heavy draw weights
 
Crossbows are actually an ancient weapon.

That they are. The oldest known seem to be southeastern Asian specimens, and after them, Chinese ones.

The evidence is still sparse, but it seems SE Asia was the origin point of the crossbow as a concept, and then it spread towards China.

Speaking about European antiquity alone, we know both the ancient Greeks and Romans were familiar with the concept of a crossbow, though both of their designs are separated by a different approach and by many centuries between their invention. And the medieval European crossbows were based on the Roman examples from late antiquity - particularly the rolling nut lock, which became iconic for euro-crossbows - not on the Greek designs.

The Inuit had a version of the crossbow

I would caution you about saying this in too cocksure a manner. There is a fair bit of material and historical evidence the Inuit knew how to make simple crossbows, the only such culture in the New World (but isolated from all the others). However, we still don't know how the Inuit acquired the idea, whether they came up with it on their own or through Alaskan, Kamchatkan and Asian trade routes, and we don't know when they adopted them. There seems to be a degree of evidence that they knew about crossbows as a concept already before contact with Europeans in the 19th century, and that the concept did not come to them earlier from Europe (potentially via Scandinavian settlers of Greenland). But we do not know the exact details. Those are lost to time and we'll probably never get a satisfying answer when and how simple crossbows first appeared among the Inuit. Most of them, especially in recent centuries, seemed to be mostly children's toys.

It would be inaccurate to say "the Inuit had no idea about crossbows", but it would be equally inaccurate to say "we know a great deal about crossbows among the Inuit".

and giant crossbows were used as siege weapons

Stationary or wheeled siege crossbows certainly were, in both medieval Europe and in China.

You had the ballista and it's descendants,there was the harpax and there might've been a repeating version known as the polybolos.

Those are not crossbows. They are torsion siege engines and they have a different spring-shooting system compared to that of archery weapons like bows or crossbows.

I wouldn't rule out poison as that can be a powerful weapon in itself. Maybe flaming bolts from either a standard size crossbow or a ballista?

Poison in Chinese repeating crossbows was a sign that their manufacturers and users didn't trust the energy transfer into the bolts enough to be sure it could kill someone or wound them seriously. Hence the poison, it was to ensure you could wound or kill an attacker.

As for flaming bolts, those are largely exaggerated Hollywood nonsense. Same with catapults throwing balls of flaming, exploding napalm.

They did use flaming or heated projectiles in the Middle Ages, but it was far less glamorous than popculture likes to portray it.


Here's a video demonstration of a longbow shooting an arrow with a steel cage arrowhead that carries kindling and a burning substance.

The arrowhead was based on a crossbow bolt arrowhead from a museum (in Switzerland, if I recall correctly). So yes, there were some specialised igniting arrowheads, but the fact we come across them fairly rarely, even in archaeological digs around castles with a history of sieges, says a lot. They had some tactical value, perhaps for psy-ops ("Ha ! Your thatched roof is burning ! Go put out the fire while we continue the siege and have less defenders to fight !"), but the idea they were widespread and standard issue is... well, dubious.



Lindybeige (Nik Lloyd) did two fantastic videos about the impracticality of fire arrows, fire bolts and "magic fire projectiles" in real historical warfare. He also shows a real longbow arrow with a "fire cage" arrowhead attached to the shaft, based on those known historical specimens (replica example here). As he notes, even historically accurate fire arrows would be quite heavy, so you can't shoot them that far. You'd need to get in close to a castle, shoot the arrow over the walls and pray that the little fire burning in the cage hits something in the courtyard it can ignite. Fire arrows would also be rubbish against soldiers.

Leonardo DaVinci had plans for a rapid fire crossbow

Which I detail above. However, the "rapid-fire" connotation is misleading. It was a fast-spanning crossbow, otherwise it was entirely ordinary. And even its spanning takes a while. Some have argued that it would be only marginally faster to span than a crossbow with a more conventional spanner. Its one clear advantage was that the spanner was built directly into the crossbow, integrated, and so you didn't have to worry about carrying it around on your belt or in a bag and potentially losing it at an inopportune moment.

and compound crossbows would be impressive.

Compound bows, necessary for such crossbows, were only made fully possible with 20th century innovations. You'd have a tough time manufacturing one even with 19th century industrial tech. (Don't take fantastical steampunk stories set in Victorian times too literally. A lot of their tech would be incapable of manufacturing certain weapons and tools, because the industrial innovations were achieved only many decades later.)

I know wrist mounted crossbows are popular in fantasy fiction,but have no idea how viable they are for the ancient/medieval time period. But it seems that crossbows in themselves are very versatile weapons with few limits.

As for wrist-mounted crossbows, you'd need industrial era advances, on the level of the late 19th and 20th century at least, to make them work. And they would not be true crossbows. The proposed designs for "wristbows" weren't bows at all, but closer to a tiny torsion throwing engine or even something like a mechanical slingshot. It would generally require parts and materials as advanced or even moreso as those of a compound bow.


Skall had a pretty good video essay/analysis on all the issues wrist-mounted crossbows would encounter. It's not only material and tech issues, but also size and performance and ergonomy issues. You can't entirely cheat physics or human anatomy. That goes for any weapon, real or fictional, historical or modern.
 
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