Pump-action

From Free net encyclopedia

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.

Pump-action shotguns far outnumber pump-action rifles in models made and in numbers sold. The Remington 870, Mossberg 500, and Mossberg 590 are the major current-production pump-action shotguns and account for a huge percentage of total new shotgun sales. Similarly, the Winchester Model 1897 and Winchester Model 1912 were sold in very large numbers during their high production years before being discontinued in 1957 and 1963, respectively. The Remington Model 7600, like its predecessor the Model 760, is the main pump-action centerfire rifle on the firearms market today.

Operating Cycle

A pump action firearm is typically loaded in a tubular magazine underneath the barrel. The rounds are fed in one by one through a port underneath the receiver and contact the carrier, a spring-loaded lever that loads rounds from the magazine into the chamber. The carrier guides rounds into the magazine until the user is done loading the weapon, at which point the carrier falls into resting position, blocking the loading port. The loaded rounds press up against a magazine follower, a cylinder inside the magazine that places tension on a magazine spring located in front of the follower. When the weapon is fully loaded the follower comes into contact with a magazine plug, a bar that extends between the coils of the magazine spring which prevents the follower from moving further.

When the magazine is loaded the shooter pulls back on the handgrips to begin the operating cycle, which ejects the empty shell from the chamber, cocks the hammer, and loads the new shell.

Pulling back the handgrips begins multiple sequences. As the handgrips are pulled back tension on the magazine spring is released, forcing the follower backwards against the rounds towards the carrier, causing the rearmost round to come to rest on the carrier.

At the same time the backward motion of the handgrips pulls a slide rail, a metal bar connected to the top of the handgrips that extends towards the receiver. The slide rail pulls back a slide located underneath the chamber. As the slide moves it puts pressure on the breech block, causing that to move backward as well. Simultaneously, it causes the locking block to move downwards out of firing position and retract the firing pin.

When the slide approaches the back of the receiver it comes into contact with the hammer, located behind the carrier, moving it downwards onto a spring. When the spring is fully compressed the sear locks onto the hammer and holds it in its cocked position. The slide then depresses the carrier dog, a switch that causes the carrier to move up and down. Upon depression it moves the carrier upwards, forcing the round the carrier is holding into the chamber.

The action after that point is completed by pulling the handgrips forward. As forward motion is placed on the slide it releases the carrier dog which springs back into rest position and causes the carrier to once again block the loading port. The forward motion also causes the bolt to move towards the front of the receiver, causing the loaded round to become fully chambered. When the handgrips are extended fully forward the weapon is locked and ready to fire.

To fire the gun the user pulls the trigger, which contacts the bottom of the sear, causing it to pull back. This releases the spring-loaded hammer from its locked position causing it to shoot forward towards the firing pin located inside the bolt. The spring-loaded firing pin then impacts the primer of the loaded shell, causing it to fire. When the shooter releases the trigger the sear is returned to its normal position by a small spring.

The empty shell is discarded when the operating cycle is re-initiated. An extractor that grips the rim of the round holds the shell towards the moving breech bolt. At the time the new round is on top of the carrier the old shell exits the firearm through an ejection port located directly above the carrier. It is shot out by an ejector spring located on the side of the receiver opposite to the ejection port. When the bolt is moved back far enough the spring is released, shooting the old shell out of the ejection port.