Pump-action
A pump-action rifle or shotgun is one in which the handgrip can be pumped back and forth in order to eject and chamber a round of ammunition. It is much faster than a bolt-action and somewhat faster than a lever-action, as it does not require the trigger hand to be removed from the trigger whilst reloading. When used in rifles, this action is also commonly called a slide action.
The term pump-action can also be applied to various airsoft guns and air guns, which use a similar mechanism to both load a pellet and compress a spring piston for power, or pneumatic guns where a pump is used to compress the air used for power. See the airgun article for information on how spring piston and pneumatic airguns work.
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[edit] Advantages
The speed of cycling of a pump-action, while less than that of an semi-automatic design, is still quite fast. The manual operation gives a pump-action the ability to cycle rounds of widely varying power that a gas or recoil operated firearm would fail to cycle, such as most less than lethal rounds. The simplicity of the pump-action relative to a semi-automatic design also leads to improved durability and lower cost. It has also been noticed that the time taken to work the action allows the operator to identify and aim on a new target, avoiding a "spray and pray" usage.
[edit] Layout
A pump-action firearm is typically fed from a tubular magazine underneath the barrel, which also serves as a guide to the movable forend, although some, notably the Remington 760 rifle and its successors, use detachable box magazines. The rounds are fed in one by one through a port in the receiver, where they are pushed forward. A latch at the rear of the magazine holds the rounds in place in the magazine until they are needed. If it is desired to load the gun fully, a round may be loaded through the ejection port directly into the chamber, or cycled from the magazine, which is then topped off with another round. Pump shotguns with detachable box magazines or even drums exist, and may or may not allow the magazine to be inserted without stripping the top round.
[edit] Operating Cycle
Nearly all pump-actions use a back-and-forward motion of the forend to cycle the action. The forend is connected to the bolt by one or two bars; two bars is considered better because it provides symmetric forces on the bolt and pump and reduces the chances of binding. The motion of the bolt back and forth in a tubular magazine model will also operate the elevator, which lifts the shells from the level of the magazine to the level of the barrel.
After firing a round, the bolt is unlocked and the forend is free to move. The shooter pulls back on the forend to begin the operating cycle. The bolt unlocks and begins to move to the rear, which extracts and ejects the empty shell from the chamber, cocks the hammer, and begins to load the new shell. In a tubular magazine design, as the bolt moves rearwards, a single shell is released from the magazine, and is pushed backwards to come to rest on the elevator.
As the forend reaches the rear and begins to move forward, the elevator lifts up the shell, lining it up with the barrel. As the bolt moves forward, the round slides into the chamber, and the final portion of the forend's travel locks the bolt into position. A pull of the trigger will fire the next round, where the cycle begins again.
Most pump-action firearms do not have any positive indication that they are out of ammunition, so it is possible to complete a cycle and have an empty chamber. The risk of running out of ammunition unexpectedly can be minimized in a tubular magazine firearm by topping off the magazine by loading new rounds to replace the rounds that have just been fired. This is especially important when hunting, as many locations have legal limits on the magazine capacity: for example, three rounds for shotguns and five rounds for rifles.
[edit] Trigger disconnectors
Modern pump shotgun designs, such as the Remington 870 and Mossberg 500, have a safety feature called a trigger disconnector, which disconnects the trigger from the sear as the bolt moves back, so that the trigger must be released and pulled again to fire the shotgun after it closes. Many early pump shotguns, such as the Winchester 1897, did not have trigger disconnectors, and would, if the trigger were held back, fire immediately upon closing. Some shooters feel this allows a higher rate of fire, and prefer models that lack this feature, such as the Ithaca 37 and Winchester Model 12.
