A crossbow is a weapon consisting of a bow mounted on a stock that shoots projectiles, often called bolts or quarrels. The medieval crossbow was called by many names, most of which derived from the word ballista, a torsion engine resembling a crossbow in appearance.
Historically, crossbows played a significant role in the warfare of East Asia since the 4th century B.C., as well as Europe and the Mediterranean. Today, they are used primarily for target shooting and hunting.
A crossbow is a weapon bow mounted on a stick (called a tiller or stock) with a mechanism in it which holds the drawn bow string. The earliest designs featured a slot in the stock, down into which the string was placed. To shoot this design, a vertical rod is thrust up through a hole in the bottom of the notch, forcing the string out. This rod is usually attached perpendicular to a rear-facing lever called a trigger or "tickler". A later design implemented a rolling cylindrical pawl called a "nut" to retain the string. This nut has a perpendicular center slot for the bolt, and an intersecting axial slot for the string, along with a lower face or slot against which the internal trigger sits. They often also have some form of strengthening internal "sear" or trigger face, usually of metal. These "roller nuts" were either free-floating in their close-fitting hole across the stock, tied in with a binding of sinew or other strong cording, or mounted on a metal axle or pins. Removable or integral plates of wood, ivory or metal on the sides of the stock kept the nut in place laterally. Nuts were made of antler, bone, or metal. Bows could be kept and ready to shoot for some time with little effort, allowing crossbowmen to aim better.
The bow (called the "prod" or "lath" on a crossbow) of early crossbows was made of a single piece of wood, usually ash or yew. Composite bows are made from layers of different materialâ€”often wood, horn and sinewâ€”glued together and bound with animal tendon. These composite bows, made of several layers, are much stronger and more efficient in releasing energy than simple wooden bows. As steel became more widely available in Europe around the 14th century, steel prods came into use.
The crossbow prod is very short compared to ordinary bows, resulting in a short draw length. This leads to a higher draw weight in order to store the same amount of energy. Furthermore the thick prods are a bit less efficient at releasing energy, but more energy can be stored by a crossbow. Traditionally the prod was often lashed to the stock with rope, whipcord, or other strong cording. This cording is called the bridle.
The strings for a crossbow are typically made of strong fibers that would not tend to fray. Whipcord was very common; however linen, hemp, and sinew were used as well. In wet conditions, twisted mulberry root was occasionally used.
Crossbows have a shorter draw length than bows, resulting in the need of a greater amount of draw force in order to store the same amount of energy. Very light crossbows can be drawn by hand, but heavier types need the help of mechanical devices. The simplest version of mechanical cocking device is a hook attached to a belt, drawing the bow by straightening the legs. Other devices are hinged levers which either pulled or pushed the string into place, cranked rack-and-pinion devices called "cranequins" and multiple cord-and-pulley cranked devices called windlasses.
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