They had repeating crossbows in ancient china. Called a chu ko nu or something.
Lever operated, pulling the lever back resets the limbs and loads another dart. There were a lot of problems with them though. For one thing the darts they fired were very light. Because of the way the lever worked the string was not pulled straight back, this puts a lot of stress on the bow limbs in a direction they are not built for.
I did a writup on upgraded crossbows some time back. It divided the crossbows into different types, this references the overall power and weight of the crossbow and most importantly, the shape. THe different types are:
Hand crossbows:
Hand crossbows are small and pistol sized. I have yet to find any historical reference to them in use, you tend to see them a lot in fantasy worlds. But we do make and use them in the modern world, for hunting and for fun. I handmade one on a lark one time and it worked pretty well. Hand crossbows are good for getting rid of vermin and "sneaky" applications. The small size allows you to aquire or track a target quickly, which is good for shooting running rabbits and rats and stuff.
For combat? Well for one thing the pistol configuration is easy and quick to aim, point and click and all that. The size of the crossbow limits the power greatly. If you use too strong a bow, the frame will probably break. To get around that you can poison your bolts or tip them with something that explodes ala D&D. Another possibility is firing something OTHER than bolts.
That hand crossbow i mentioned earlier? I managed to make and fire a small paper plane, which is interesting but i cant imagine how that would be useful but perhaps you guys can thing of something, messages at the very least.
Arm crossbows:
Instead of a wooden stock, the bow and track is strapped to your arm. I know this seems impractical but it actually works out quite well. Because of how the crossbow is mounted the recoil travels directly up your arm, aiding accuracy. At the same time, you need only one arm and hand to steady the weapon, your offhand can do something else like hold a shield.
The only problem? these things are a bitch to reload! Putting the bolt into place is not as hard as pulling the string back because of the arckward position. However since most crossbows nowadays are lever-cocked i would be pretty easy to rig up a system where you could rerock the crossbow by folding and unfolding your arm. This would allow you to operate the xbow one handed if you added a bolt magazine.
Hunting crossbows:
War crossbows:
Hunting and war crossbows are essentially the same thing. The only difference is how strong the bow limbs are. Hunting crossbows are weaker but generally can be recocked by hand. War crossbows are stronger but take more effort to reload which is not a problem for a trained soldier.
Because they are the same size, you can make both types of bows and swap them out depending on what you need the crossbow for.
Siege crossbows:
These hit HARD. The bolts they fire have to be reinforced or else they will shatter when you try to launch them. Siege crossbows are too bulky to move and shoot with and reloading them takes a long time. Thus they are only fit for repelling or carrying out a siege. A single bolt fired by a crossbow like this will go through most targets without stopping. They can also be used to attack people inside weak buildings, such as those made of thin wood.
If we divided crossbows like this ist would make it possible to assemble crossbows by component. Right now we have crossbows that are assembled from only ONE type of material, which is rather confusing.
Smiths would make the metal bows, bowyers would create the stocks. I suppose a carpenter could also make the stock, same skills and everything. Mechanics could create more complex parts like the trigger assembly. The bowyer is the one who puts the parts together. More importantly he makes sure that they all work properly together, something that requires specific skills.
[ September 25, 2007: Message edited by: Tamren ]