Chinese Repeating Crossbow

Recreating an ancient "burp gun"

1999

Crossbow

Crossbow, from the side

Crossbow, from the side

A very crude and simple reproduction of a crossbow illustrated in The Book of the Crossbow.

This crossbow was one of the earliest repeating weapons. By cranking the cocking handle rapidly back and forth, a stream of crossbow bolts are fired.

Crossbow and bolts

Crossbow and bolts

Construction is extremely crude - the stock ("tiller") is laminated from plywood.

The bow ("prod") is made from a single piece of ash. It's a flat bow, curved only by tension in the bowstring. The design of crossbow really needs a steam-bent bow with a little more curve to it, to reduce tension (and thus friction) when the bow is uncocked and the magazine is sliding forwards. I know very little about bowmaking and this is the least effective part of this crossbow.

The bowstring is several loops of Kevlar bowstring, a loosely-twisted waxed roving. To resist wear, the central section is served with a wrapping of more bowstring.

Bolts are cheap chopsticks, either bamboo or plastic. They're cheap and disposable! Despite the very poor bow I'm using, it still has enough energy to shatter a plastic chopstick.

Action

The crossbow is a manually-cranked repeater. A large handle on the top is racked back and forth. Bolts are fired from the box magazine, which holds up to a dozen.

There is no manual trigger mechanism. As soon as the action is fully cocked ("in battery"), the nut fires automatically.

Cocking the crossbow - Moving the magazine forwards
Moving the magazine forwards
Cocking begins by pushing the handle forwards. The whole box magazine and firing tray move forwards together, sliding over the stock. The bowstring slides backwards along a groove beneath the magazine and underneath the bolts.
Cocking the crossbow - Fully forward
Fully forward
When the magazine is fully forward, the bowstring drops into a notch at the back of the firing groove. The bowstring is now behind the lowest bolt.
Cocking the crossbow - Drawing the bowstring
Drawing the bowstring
Bringing the handle back pulls the magazine back, drawing the bowstring (trapped in the notch) back with it.
Cocking the crossbow - Almost firing
Almost firing
As the magazine returns to battery, a small peg in the base of the magazine is pressed upwards by the stock. This peg pushes the bowstring out of the retaining notch, and releases it to fly forwards, firing the bolt.

Links

Source Material