pneumatic. This is both an old and a new design; some of the earliest airguns, such as the model carried by Lewis and Clark, were of this type, as are many new cutting edge models. The precharged pneumatic uses an external source of compressed air, either an external pump or a high pressure reservoir such as a SCUBA tank, to fill a reservoir. The reservoir can be a small, single-shot one, such as in the Brocock Air Cartridge system, or a large, multi-shot tank. The key to top accuracy in a precharged pneumatic is a consistent pressure. With multishot systems (as are most), the pressure in the reservoir will drop with each shot fired, so the best way to achieve consistency is with a pressure regulator, which provides a steady, but lower, pressure at the valve, for as long as the reservoir pressure remains higher than the regulated pressure. Regulators are also generally adjustable, so a low pressure setting will provide many shots of lower power, while a high pressure setting will provide a few high power shots. Piston Piston airguns, often called "springers", are unique in many ways. Since the firing process involves a fairly massive piston suddenly moving to compress the air, they have a significant "kick", generally called "recoil" (though this is not the same as firearm recoil). The recoil begins when the piston starts to move forwards, which pushes the rest of the gun backwards. The recoil then stops suddenly as the piston reaches the end of its travel, and is brought to a stop by the cushion of high-pressure air trapped between the piston and pellet. This recoil can be brutal on the gun in high-powered models, and will loosen screws, shift sights, and break scopes not designed specifically for the unique recoil of piston airgun—all of these can lead to poor accuracy. In addition to the recoil, piston airguns have a long lock time, as the piston must compress the air before the pellet begins to move, and the gun is moving due to the recoil during this time. Spring airguns require a special technique to fire, to ensure that the gun moves very consistently during this recoil. The preferred method is a very loose hold, to allow the gun to move back; this means that a piston airgun will not shoot the same from a bench. All accuracy testing and sighting in must