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.
[1] Powerheads are available that chamber a variety of handgun, rifle, and shotgun cartridges, from .22 WMR to 12 gauge and larger.
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.
[citation needed] A common misconception of how powerheads function is that the muzzle blast does the damage, as much high-pressure gas is forced into the flesh of the target.
[1][2] In Australia they are classed as category A firearms requiring a legitimate reason for issuance of a permit to acquire to a weapons licence holder.
In the US, the ATF considers a powerhead a firearm if it is not permanently affixed to a shaft; generally powerheads are sold spot welded to a temporary steel shaft giving an overall length of greater than 18 inches (45 cm).
This means that powerheads may still be under the authority of the 1968 Gun Control Act with regard to shipping them and purchase of them from licensed dealers.