Pump-action Crossbow, Weapon theory. Options Track this topic Email this topic Print this topic Download this topic Subscribe to this forum Display Modes Switch to: Outline Standard Switch to: Linear+

[FuelDrop]

Technically I want to know this for non-shadowrun reasons and I'm here because if there's one place I can rely on people knowing this stuff it's Dumpshock, but since Shadowrun includes self-loading crossbows I might as well throw it in as a shadowrun question:

How workable is a pump-action crossbow compared to a conventional repeating crossbow, for both draw strength and rate of fire. Also, would it be viable to compare such a weapon to the electric crossbows in Shadowrun if made for/by a character who for whatever reason wanted a non-electric version?

[ShadowDragon8685]

Well, I talked a D&D DM into letting me fluff a Repeating Crossbow (which is normally lever-action) into a pump-action one. It would probably be hard to properly draw a full-strength super-strong crossbow with a pump action, but if it was weaker, akin to a Chinese repeating crossbow's pull strength, quite possible. And thankfully, most game systems that acknowledge the existence of repeating crossbows usually make them a strictly-superior choice without any damage loss, so go nuts! (IMG:style_emoticons/default/smile.gif)

[FuelDrop]

Well, I talked a D&D DM into letting me fluff a Repeating Crossbow (which is normally lever-action) into a pump-action one. It would probably be hard to properly draw a full-strength super-strong crossbow with a pump action, but if it was weaker, akin to a Chinese repeating crossbow's pull strength, quite possible. And thankfully, most game systems that acknowledge the existence of repeating crossbows usually make them a strictly-superior choice without any damage loss, so go nuts! (IMG:style_emoticons/default/smile.gif)

I was actually thinking that if you had the system so that the whole pumping action (IE back and forwards) was used to recock the bow then it'd be strictly superior to a hand drawn crossbow, theoretically allowing about twice the poundage if I'm envisioning the gearing right (In practice it'd be less, probably about 1.5 times the poundage of a hand-drawn bow, due to energy loss to friction ect).

Could someone with a bit more experience in engineering do the math for me? I just eyeballed it and have little practical experience in this sort of thing (IMG:style_emoticons/default/frown.gif)

[Sendaz]

You have to remember that the old style repeater crossbow used the lever action to get the added torque, but I do not see you getting added force from the sliding pump by itself, it being about the same as you just pulling back by hand.

Maybe through some playing with differential gears to take the increased length of the stroke of front to back & back to front with the full pump you could increase the pull, putting it on par with the lever, but again I do not se it surpassing it in power with a single pump. The only advantage being you don't need the added space to ratchet a lever in.

[qis]

When arguing about weapons, I use Youtube videos to explain relations and mechanics. Here is a very detailed one about crossbows.

Youtube: A beginners guide to crossbows (Tutorial)

There are many other videos as well. The difference between crossbow pull strength is astonishing. Some even need a pulley with a crank to be drawn by a mortal man. I'd argue that a troll can use pump action to draw one of those.

Youtube: Tactical Assault Crossbow! PSE TAC15 Upper for the AR15

[binarywraith]

Maybe a pneumatic or hydraulic assisted pump? Either way, I doubt it'd be a pump stroke you'd want to pull one handed with the thing shouldered. (IMG:style_emoticons/default/biggrin.gif)

[Umidori]

Somewhere I have a .pdf of a scan from a 1950s edition of Popular Mechanics which has detailed plans for building a five shot repeating crossbow using a 20 pound practice bow. The "pump" is just a wooden handle on a slide, designed to give you solid purchase on the constrained string and to cycle the ammunition feed.

A 20 pound bow is quite weak, though. A crossbow meant for anything more than hunting small game is going to take a lot more force to draw, easily hitting 60 to 80 pounds for a reasonably strong crossbow. For something that is intended for combat against armor of any sort, one need look to historical examples from the Rennaisance and Medieval periods, in which 100 to 140 pounds were not unheard of, and some larger weapons actually hit 200 or 300 pounds of draw force.

None of these are "pumpable" though. It's just not a very efficient way of drawing the string for a crossbow, as it offers very little mechanical leverage. I suppose you could have some sort of pulley and rachet system, offering enough mechanical advantage to let you draw the bow a reduced distance per pump at a reduced output of effort per pump, but then you need to cycle the pump repeatedly to achieve a full draw. This could be compensated for somewhat with a "lever-action" design, which (unsurprisingly) provides more leverage, allowing each pump to be more productive, but at this point you might as well be using an antique "cranequin" like they did way back when.

Really, the primary benefit of a crossbow over a bow has always been the ease of aimming and the ability to keep a powerful shot ready in advance without having to hold the bow drawn (which quickly can tire you out). The tradeoff has always been slow rate of fire and reload. There's just not any real way to speed up the drawing of a high-weight bow, short of using electric motors and whatnot.

~Umi

[qis]

Some guys in my gym have no problem pulling over 140 pounds with one arm. Give them cyberware or adept spells and this number will go up. I could think of a few in-house rules to allow such crossbows - that would be fun! Speaking of in-house rules, throwing spears could be fun too...

[Umidori]

What do you mean by "pulling 140 pounds with one arm"?

There's a vast difference between a 140 pound deadlift and a 140 pound arm curl. Picking up 140 pounds off the ground with one arm actually uses your entire body - arm, shoulders, back, abdomen, hips, legs - all braced against the ground. Curling 140 pounds uses mostly just your biceps and triceps (although the rest of your body is used for purposes of rigid bracing).

Drawing a regular bow distributes the weight of the pull across both arms and your shoulders, as you are "inside" the bow and string, and you draw by spreading and pushing your limbs outwards. Drawing a crossbow is entirely different. You don't have a primary grip on the bow, but rather on the stock, while your other hand overreaches to grasp the string, and you have to awkwardly push and pull the leverage points toward each other. You're working against your own leverage.

Hence why crossbows developed various mechanisms for shifting or increasing your leverage. Stirrup crossbows allow you to anchor the bow with your foot, placing you once against "inside" the bow and string, and you draw by stretching outwards. Lever crossbows, unsurprisingly, use simple levers to shift the point of leverage, producing much the same effect. Cranequin crossbows use a rack and pinion to transform rotary motion into ratcheting lateral motion. And windlass crossbows combine a super sized cranequin with a stirrup, offering the most leverage of all.

So a 140 pound pull of a stirrup crossbow "with one arm"? Totally can see that. But a 140 pound shotgun style pump? That would require much, much more strength, because it has terrible mechanical advantage.

~Umi

[FuelDrop]

I found a website claiming that the highest poundage bow IN THE WORLD is 225 lb draw.

I'm calling BS on that right away, primarily because a bit down that very page was an ad for a 260 lb draw crossbow. Anyone got actual figures for the upper limit on crossbow draw strength?

[Always Overkill]

What do you mean by "pulling 140 pounds with one arm"?

There's a vast difference between a 140 pound deadlift and a 140 pound arm curl. Picking up 140 pounds off the ground with one arm actually uses your entire
body - arm, shoulders, back, abdomen, hips, legs - all braced against the ground. Curling 140 pounds uses mostly just your biceps and triceps (although the
rest of your body is used for purposes of rigid bracing).Drawing a regular bow distributes the weight of the pull across both arms and your shoulders, as you
are "inside" the bow and string, and you draw by spreading and pushing your limbs outwards. Drawing a crossbow is entirely different. You don't have a primary
grip on the bow, but rather on the stock, while your other hand overreaches to grasp the string, and you have to awkwardly push and pull the leverage points
toward each other. You're working against your own leverage. Hence why crossbows developed various mechanisms for shifting or increasing your leverage.
Stirrup crossbows allow you to anchor the bow with your foot, placing you once against "inside" the bow and string, and you draw by stretching outwards.
Lever crossbows, unsurprisingly, use simple levers to shift the point of leverage, producing much the same effect. Cranequin crossbows use a rack and pinion
to transform rotary motion into ratcheting lateral motion. And windlass crossbows combine a super sized cranequin with a stirrup, offering the most leverage of
all. So a 140 pound pull of a stirrup crossbow "with one arm"? Totally can see that. But a 140 pound shotgun style pump? That would require much, much more
strength, because it has terrible mechanical advantage.

~Umi

That's one fine forensic analysis of the physics surrounding drawing a bow as opposed to those involved in reloading a crossbow Umi.

[Tymeaus Jalynsfe...]

I found a website claiming that the highest poundage bow IN THE WORLD is 225 lb draw.

I'm calling BS on that right away, primarily because a bit down that very page was an ad for a 260 lb draw crossbow. Anyone got actual figures for the upper limit on crossbow draw strength?

Don't know about upper limits- My Stepfather built one out of a short Heavy Duty Truck Spring that theoretically clocked in at almost 400lbs Draw per the Popular Mechanics book he built it from. Not sure how accurate the Specs would have been for that draw weight, but it had a Foot stirrup and massive lever. In comparison, my 85 lb. Draw Hunting Bow was a beast to use, even as an adult.

[binarywraith]

Don't know about upper limits- My Stepfather built one out of a short Heavy Duty Truck Spring that theoretically clocked in at almost 400lbs Draw per the Popular Mechanics book he built it from. Not sure how accurate the Specs would have been for that draw weight, but it had a Foot stirrup and massive lever. In comparison, my 85 lb. Draw Hunting Bow was a beast to use, even as an adult.

The only real upper limit is how big you want to build it, and the tensile strength of your materials. The Romans built ballistae in the 4th century that could throw a 24kg bolt for over 1000 yards.

[Tymeaus Jalynsfe...]

The only real upper limit is how big you want to build it, and the tensile strength of your materials. The Romans built ballistae in the 4th century that could throw a 24kg bolt for over 1000 yards.

True... (IMG:style_emoticons/default/smile.gif)

[Umidori]

I found a website claiming that the highest poundage bow IN THE WORLD is 225 lb draw.

I'm calling BS on that right away, primarily because a bit down that very page was an ad for a 260 lb draw crossbow. Anyone got actual figures for the upper limit on crossbow draw strength?

There probably have been very few traditional bows in the range of 225 pounds of draw, because very few humans have historically been both able and willing to draw a bow of that weight without additional mechanical advantage. There might be heavier examples somewhere, but you'd need to be one of the strongest people in the world to use such a weapon, so it might as well be the heaviest bow in the world, and it quite certainly could be the heaviest bow currently in production somewhere.

A 260 lb crossbow is not unheard of, I've researched historical examples within that range, although it's still a pretty heavy draw weight for a "man portable" weapon intended for use by a single operator. Of course, since you cite an advertisement, obviously the crossbow in question is a modern day one, and while I'm not familiar with contemporary draw weights, I imagine with modern materials it's an entirely reasonable weight... for a crossbow. (IMG:style_emoticons/default/wink.gif)

Yes, technically a crossbow is a bow, merely fixed on a stock, so technically any 300+ pound crossbow by definition employs a 300+ pound plus bow in its construction. But for the sake of clarity of meaning, bows and crossbows are separate devices, and they have separate values of realistic draw weights.

~Umi

[FuelDrop]

There probably have been very few traditional bows in the range of 225 pounds of draw, because very few humans have historically been both able and willing to draw a bow of that weight without additional mechanical advantage. There might be heavier examples somewhere, but you'd need to be one of the strongest people in the world to use such a weapon, so it might as well be the heaviest bow in the world, and it quite certainly could be the heaviest bow currently in production somewhere.

A 260 lb crossbow is not unheard of, I've researched historical examples within that range, although it's still a pretty heavy draw weight for a "man portable" weapon intended for use by a single operator. Of course, since you cite an advertisement, obviously the crossbow in question is a modern day one, and while I'm not familiar with contemporary draw weights, I imagine with modern materials it's an entirely reasonable weight... for a crossbow. (IMG:style_emoticons/default/wink.gif)

Yes, technically a crossbow is a bow, merely fixed on a stock, so technically any 300+ pound crossbow by definition employs a 300+ pound plus bow in its construction. But for the sake of clarity of meaning, bows and crossbows are separate devices, and they have separate values of realistic draw weights.

~Umi

My apologies, I misquoted. Yes, the website specified a 225 lb draw crossbow as the heaviest in the world before blatantly contradicting itself.

[Umidori]

Well, then the website is just stupid? It IS the internet, after all... (IMG:style_emoticons/default/nyahnyah.gif)

~Umi