A powerhead is a specialized firearm used underwater that is fired when in direct contact with the target. Powerheads are often used for spear fishing and against sharks or alligators for sport, defense, or to kill nuisance animals. The term powerhead refers to the firearm-like part of the device; when attached to a shaft to form a spear, it may be referred to as a bang stick or shark stick. The spear in question may be handheld or launchable from a spear gun. Design A powerhead consists of a length of tubing which is the chamber for the cartridge, a firing pin to fire the cartridge, and usually some form of safety pin or latch that prevents firing when it is engaged. The rear of the power head is fitted with some provision for attaching to a spear. Powerheads are available that chamber a variety of handgun, rifle, and shotgun cartridges, from .22 WMR to 12 gauge and larger. .357 Magnum is probably the most common, as it is fairly powerful yet still compact enough to be used in a spear gun. Large cartridges such as the 12 gauge are generally only used on a handheld spear. Some powerheads use the cartridge to propel a barbed spear point into the target. These are generally used on a bangstick for alligator hunting, to secure a line to the alligator to prevent escape. Purpose of contact-shooting Bullets are generally designed to work in air, which has a very low density. The density of water is roughly 800 times higher than that of air at sea level, and that reduces the penetration of a bullet proportionally. A bullet might travel a mile (1.6 km) in air, but travel no more than a few feet (about a meter) in water. Expanding hunting or defensive ammunition, such as that using hollow point bullets, will penetrate even less, as the water is dense enough to cause the bullet to expand. By firing while in contact with the target, a powerhead does not waste energy on traveling through the water, but rather expends all its energy directly on the target. How they work Although most commercial powerheads use standard handgun ammunition, such as .357 Magnum or .44 Magnum, many users choose to use larger caliber ammunition to do maximum damage to the intended target. A common misconception of how powerheads function is that the muzzle blast does