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I'm writing a story about a modern age HEMA medievalist who time travels to the Viking age.

Is it possible to make a crossbow with similar performance to modern age crossbows without using modern materials such a aluminum, nylon and carbon fibers?

I'm expecting a result to be something with wooden frame, horn and sinew limbs, and steel cams & wheels. Cocking mechanism could be omitted if unfeasible.

I'm assuming that all technologies are available in that time from across the whole of Eurasia (metallurgy, bow-making) would be accessible (and can be traded for).

I'm looking for something with similar performance to the modern crossbow which has 470 FPS / 182 FP (246 Joules) of kinetic energy.

For comparison :

  • Medieval longbow (95 lbs draw weight); 45 Joules
  • Medieval crossbow (450 lbs draw weight); 53 Joules
  • .22 LR; 168 Joules
  • 9 mm; 467 Joules
  • .308; 3,217 Joules

Source Tod's Workshop

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  • $\begingroup$ When you say Euroasia, are you including access to silk? $\endgroup$ – BLT-Bub Mar 18 at 17:23
  • $\begingroup$ Yes everything from the old world $\endgroup$ – kelari4377 Mar 18 at 17:28
  • $\begingroup$ why not windlass crossbow instead ? i believe even with windlass crossbow it will be overkill for viking age armor and shield to withstand. just in case, iam not the one that downvote you. $\endgroup$ – Li Jun Mar 18 at 17:37
  • $\begingroup$ @LiJun It's useless due to short power stroke youtube.com/watch?v=TdB470lo6nM $\endgroup$ – kelari4377 Mar 18 at 17:46
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    $\begingroup$ what kind of enemy you face ? are they human? they use apropriate viking age armor and shield right ? like chainmail ? or do you want speed ? the the closes alternative is zhuge nu or repeating crossbos as other has bring up. but as i say even for windlass crossbow its already overkill for that age armor and shield, since viking shield is thin and use center grip. the rest is depend how you applied it to be effective, like formation,strategy/tactic,landscape,trap, etc. $\endgroup$ – Li Jun Mar 18 at 18:08
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Is it possible?

I think it should be possible. The force for the projectile is still held in the bow for the most part, right? The cam and wheels just allow for a different orientation for the device.

The idea of a cam predates the viking age significantly. Miniaturizing it might be a challenge, but let's not discount the skills of the blacksmiths of the age, if the goal is described to them I think they could pull it off. Your guy isn't a HEMA professional, right? I don't think there are many of those. Maybe his day job is mechanical engineering or machining.

Based on this sales pitch, the main benefits are

  • better weight distribution

  • slightly longer powerstroke, for size

  • a stabler and quieter shot

So, this isn't going to produce some crazy armor decimating device. Because the force is still held in the bow, and your guy probably isn't going to bring some massive material science advantage with him, this will just give his team access to bows that they could have designed previously, but they would have been slightly large and awkward to aim.

Why didn't it already exist?

On a per capita basis medieval people spent way more time thinking about killing each other than we do (citation hopefully not needed), so these question always come with the built in: why didn't they invent your guy's new idea for a weapon?

I think it is plausible in this case, though. The main benefits are easier aiming for precise shots. The crossbows they had were mechanically much simpler, which is a huge production and maintenance advantage. For war, we expect the soldiers to mostly be firing in formation anyway, so precise shot accuracy for targeting individuals is not a huge priority. For hunting, bows do just fine. Your market is mostly peasants (nobles too, but they are hunting for sport mostly -- they aren't interested in totally optimizing the productivity of their hunting experience, they won't revolutionize bow design to support a hobby). Miniaturized cams will probably require a skilled blacksmith, so you aren't swimming in the things.

In addition, technology development is largely evolutionary in most cases. I don't think traditional crossbows + cams are enough of an advantage to be mass produced. The weight distribution benefit of changing the orientation of the bow isn't immediately obvious, and the orientation change is a pretty big leap. So, it seems plausible that nobody thought to do it until machinists started seeing the prerequisits everywhere in their day-to-day lives, and one of them happened to be a hunter.

You at least have plausible deniability, here.

What good is it?

I suspect that you'll need to at least get the best blacksmith in a large town/small city on board with this plan. You aren't mass producing these things in every little village across the land. Plus, they are more mechanically complicated. So, I don't think you are arming your whole army with these things. These will be your medieval Designated Marksman's Rifle. Plus, they are all hand crafted by blacksmith unfamiliar with the tech so there will be lots of quality variations, especially at first.

Presumably, your guy is also bringing some modern tactics. Perhaps you can arm a small squad of troops with the bows that randomly ended up highest quality, and use them to sneak up on the enemy camp beforehand and take out the leadership. Your superior range, quietness, and pinpoint accuracy will come in handy here. (also, you can probably copy some other modern features, like the bipod). You can probably also embed a couple of guys with the special bow into your crossbow units to take aimed shots at high value targets during battles. A nice perk of this is that the device isn't so obviously weird that the guy will stick out from afar, so to your enemies it will just feel like a weird coincidence that the guy carrying the signal flag seems to always get shot first thing every battle.

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    $\begingroup$ i cant even imagine what kind of martial arts practitioner/duelist that focus in using crossbow, i guess maybe the predecessor of Gun Fu $\endgroup$ – Li Jun Mar 18 at 18:57
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    $\begingroup$ If they could produce those things in enough quantity and any peasant with rudimentary training could kill knights & mounted archers from 300 meters say goodbye to chivalry & steppe empires. The history would be far different. $\endgroup$ – slobodan.blazeski Mar 18 at 19:10
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    $\begingroup$ While I appreciate the checkmark, it is preferable to give the question a good 24 hours before picking the answer. Give Asia a crack at the question, somebody there probably has a cool crossbow idea, given that historically they had some cool crossbows. :) $\endgroup$ – Zwuwdz Mar 18 at 19:21
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    $\begingroup$ @slobodan.blazeski i doubt about steppe empire will fall they face china, which majority use crossbow outside of gunpowder weaponry, even the peasant equiped with repeating crossbow dipped with poison, for chivalry thats what the pope is, they ban the weapon that can kill knight which happen to be crossbow and dagger. $\endgroup$ – Li Jun Mar 18 at 20:21
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    $\begingroup$ @slobodan.blazeski here found some discussion about it, i dont check it yet. twcenter.net/forums/… and this myarmoury.com/talk/viewtopic.31967.html $\endgroup$ – Li Jun Mar 18 at 20:54
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While the parts themselves can be replicated using medieval tech they have nothing to do with a bow's maximum velocity.

Where maximum velocity comes from:

Your materials have various properties depending on if they are in the belly or backing of the bow that determine it's snap. More snap means a higher base acceleration. Wooden bows tend to have a lower snap than something like fiberglass; so, medieval archers compensated for this with arm length. This works up to a certain scale because the snap is compounded across the length of the arm. Arm length compounded with materials determines the ideal maximum velocity.

What about draw weight and length?

These are important factors behind a bow's power but not speed. A bow with a lower draw weight will receive more relative resistance from the weight of your arrow meaning a bow with a higher draw weight can more effectively fire a heavy arrow, and will shoot a little bit faster because it can better overcome the arrow's inertia, but still caps out based on the material limitations. It's like this: a strong man can not throw tennis ball much faster or farther than a weaker man with similar technique, but a strong man can throw a bowling ball much faster and farther because he can overcome the weight better.

Medieval war arrows were on average 2-3 times heavier than hunting arrows so they could better penetrate armor which is why draw weight was so important on a warbow.

Draw-length is similar to draw weight in that it mostly contributes to doing a better job of reaching the maximum velocity that your snap allows. A greater draw length gives you more time to accelerate the arrow allowing you to reach closer to your ideal maximum velocity before it leaves the bow, but again, does nothing to increase the ideal maximum velocity.

So where does this leave you?

Since the viking age mostly predates spring steel, fiberglass, etc, the fastest bows you can really achieve will probably be just over 200 FPS using either a bamboo and hardwood composite or a horn and sinew composite. Neither of these materials would particularly benefit from the compound bow or reverse draw crossbow design. Compound bows need to take advantage of modern materials that bend very little but have LOTS of snap, traditional materials have too much bend for this. The reason for reverse draw crossbows is because those same materials have more snap in the compresion state than the tension state. In contrast, most traditional materials get more of thier driving force from the tension of the backing material than the compression of the belly material; so, inverting them to be compression dominate would make them worse.

If you want a better projectile speed/range, the Roman manuballista and scorpions could hit speeds much closer to a modern crossbow using coiled sinew cords, but again, it's design would not benefit from the compound or reverse draw mechanisms. Vikings could almost definitely make them if they tried, but they were really heavy weapons compared to bows or crossbows; so, the trade-off is only worth it in certain cases.

If you fast forward to the later medieval era though, you will see spring steel crossbows start coming into play. These were limited to very short draw lengths because the arms could not bend much, but they had tons of snap and draw weight. If you were to add compound or reverse draw mechanisms to these, then you would be able to achieve something much closer to a modern crossbow without having to make something too heavy. That said, spring steel was never an easy thing to make, even in the late medieval period, it took a highly experienced smith to properly temper the steel without the use of modern high temperature thermometers.

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  • $\begingroup$ What's the limitation on spring steel? Is it something that a well informed modern person could bring back (just throw a 'lil bit more or less carbon in the fire), or is it some deep material-science mysteriousness? $\endgroup$ – Zwuwdz Mar 18 at 20:52
  • $\begingroup$ Could you please provide some references, otherwise this seems like it should be accepted answer. $\endgroup$ – slobodan.blazeski Mar 18 at 21:22
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    $\begingroup$ @Zwuwdz First you need a homogenized medium-to-high carbon steel (wrought steel will generally have too many impurities and too little carbon to perform well in this context). This means knowing how to get a furnace hot enough to melt the iron into its liquid state so you can skim the slag and manually control the carbon content. You also need to know how to make a ceramic crucible with a higher melting temperature than the steel you are firing. Some but very few Viking smiths had the know how and resources to do this... $\endgroup$ – Nosajimiki - Reinstate Monica Mar 19 at 1:27
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    $\begingroup$ Once formed, your arm needs to be quenched to make it hard, then tempered to make it springy. It could all technically be done in the viking age but without modern furnaces, thermometers, and computer controlled kilns, it was a very skillful and expensive process that only a handful of master smiths could probably figure out even with the science explained to them. $\endgroup$ – Nosajimiki - Reinstate Monica Mar 19 at 1:27
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    $\begingroup$ I'd like to note that the Greeks ran into this material limit centuries before the Viking age and solved it by using torsion springs instead. Although they, and Romans, only used this for siege weapons. Not sure if anyone tried scaling it down. Increasing the power of your hand bow is not as useful as you'd think. $\endgroup$ – Ville Niemi Mar 19 at 16:03
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Is it possible to make crossbow with similar performance like the modern age crossbows without using modern materials such a aluminum, nylon & carbon fibers?

I'm expecting result with something with wooden frame, horn & sinew limbs, and steel cams & wheels.

Obviously no, I would say else it would have been made already in those times, since those very materials you cite were used. Don't forget that weapon making and improving has always been a very prized profession, and improving an existing weapons would have granted a good reward.

If you want modern performance, you need to use modern materials.

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  • $\begingroup$ I appreciate what you're saying but every weapon has to have a first. $\endgroup$ – Lio Elbammalf Mar 19 at 13:02
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    $\begingroup$ There are other possibilities for it not having been done than "not possible to do". One that leaps to mind is it might be possible but impractical. A weapon that takes man-years to make (and perhaps is subject to breakage) would only be useful to the very rich. $\endgroup$ – T.E.D. Mar 19 at 14:51
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It might be possible, but you are not going to get any better performance out of it than crossbows at the time, likely far worse.

Steel cams are heavy and likely beyond viking technology, bone or wood ones will not hold up to the stress, so you are looking at copper or bronze, which is again heavy, stealing a lot of energy from the bow and subjecting the arms to very high stresses. You also don't have modern machining to get smooth bearings so you loose a lot of energy and get a lot of wear and tear. Worse they have no way to produce a strong enough frame, you can't use wood becasue the frame is withstanding a lot of tension, which means everything frame,limbs, and cams needs to be made of metal, which means more losses of energy and you will not be lifting and using this device even if you could make it. All together energy you lose in material mass and bearings means the cams don't give you any advantage.

Now keep in mind 2000+lb medieval crossbows exist, although they are also likely beyond what the viking could produce. Which would work like the cranequin below. Which were also pushing the limits of what medieval steel and wood could withstand.

enter image description here

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    $\begingroup$ ah yeah cranequin, i was trying to remember this one too but i only remember the windlass one. $\endgroup$ – Li Jun Mar 18 at 18:17
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Your time traveler can always resort to the repeating crossbow. It's not as effective as a modern, but for that age, it is effective, easy to build with the materials at hand, and easy to use.

enter image description here

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I'll offer a bit of a frame change.

A compound bow, using a system of cams or other devices, is not intrinsically more powerful than an ordinary bow. English and Welsh longbowmen used warbows with draw weights of between 100 and 120lbs (enough to cause distinctive warping and other changes in their skeletons), while by the 1400's, steel crossbows with draw weights of 1200lbs were in service, requiring the use of a winch spanning mechanism to draw. Only hobbyists make things like that today, few commercial hunting bows approach anything like that amount of draw weight.

enter image description here

A lighter crossbow drawn by hooking the string to a belt and using the muscular strength of the legs

The purpose of the cam mechanism in a compound bow is to "let off" the maximum draw weight. A 75lb hunting bow will require a draw of 75lbs, but once past the point where the camming mechanism kicks in, the actual weight the hunter has to apply to keep the bow drawn is much less. This makes aiming and releasing much easier (and since few people have been training with bows since boyhood, the skill to rapidly draw, aim and shoot a high draw weight bow is not very common).

Since a war crossbow is already mechanically cranked and then "locked" into full draw by the trigger mechanism, and the archer is going to loose rather quickly, there is little benefit for having a compound bow mechanism. Archers are not waiting in a tree rest or blind waiting for an animal to appear, rather they are in ranks between men at arms or pike squares drawing and loosing as quickly as possible or practical at massed targets before them.

So while it may be possible for Viking era bowyers to apply laminations to wood, or experiment with steel to make more powerful crossbows, eventually the limits of that era's material science is going to be reached. Bows of any era were generally as powerful as possible given the materials at hand and the archers who could use them.

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Seems to be doable though we don't know how expensive or cumbersome this device would be.

Cams and draw mechanism are out of reach of Viking technology, so let take Bulldog 440 as a target. bulldog crossbow

I assume that wooden frame is possible since there are 1200# crossbows made of wood, Vikings could definitely make something like modern frame though heavier.

420# draw weight is possible to be drawn with stirrup & doubler belt. 8:54 https://youtu.be/2IdfmaC_t-Q

Trigger would be primitive but usable.

There was traditional recurve bow with 200# draw weight so I assume 300# limbs are plausible.

Turning the limbs around will increase your power stroke, which will increase your efficiency, however craftmanship need to be top notch to avoid 300# limbs cracking in front of your nose. Consult experienced bowyer for opinion. I think I read somewhere that excalibur tried that but hunters find them uncomfortable.

The last problem is that traditional limbs would be very heavy and inefficient compared to modern ones. This is something that you can't surmount without modern materials. Your crossbow would be slower & less efficient than a modern one.

All in all you might make the best crossbow in that period but it would be far from a modern one. With twice the draw weight of a longbow & 66% of its power stroke it might be enough to change history toward infantry if you could mass produce it.

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