the damage, as much high-pressure gas is forced into the flesh of the target. While the gas does do some minimal damage, it is ultimately the penetration of the slug that causes the damage to the target. Most powerheads function just as traditional firearms do, except that it is the spear which acts as the firing hammer. One commercially produced version used a modified .30-30 Winchester cartridge case, loaded backwards, with a primed .38 Special case loaded in its mouth holding the primer. The cartridge was loaded with the .30-30 case facing outwards, so that the .30-30 case full of burning powder was propelled into the target upon firing. This system is fast to reload and one of the most effective despite the fact that it does not use a bullet. Ammunition issues Since most powerheads are designed to use commercial ammunition, which is not designed to be used underwater, the ammunition used must be waterproofed. A coating of nail polish or varnish is commonly used around the primer and case mouth. For shotshells, a layer of rubber, such as a balloon, can be used to seal the crimped front of the shell. Legal issues Australia 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. When not in use, they must be safely stored in a locked container with ammunition stored separately. Regulations vary between states, with some states permitting their use for defense against sharks only, and not for spearfishing. United States A powerhead may be considered a firearm under some circumstances. 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). After installing permanently on a spear shaft, the spot weld is cut, and the temporary shaft discarded. Revenue Ruling 55-569, C.B. 1955–2, 483 says: This ruling is with regard to the National Firearms Act, and not to the 1968 Gun Control Act. (The National Firearms Act defines 'firearm' as machine guns, short barreled rifles, short barreled shotguns, and concealable firearms that are neither pistols nor revolvers.) This means that powerheads may still be under the authority of the 1968 Gun Control Act with regard to shipping them and purchase of