Semiauto Actions
Sometimes refererred to as a selfloading firearm. When the trigger is pulled these firearms utilize the recoil or hot gases generated by the cartridge to eject the fired cartridge case, recock the gun and compress a spring in the action. After the bolt or slide has reached it rearward travel, the compressed recoil spring will push the bolt or slide forward loading a new cartridge into the chamber if there is one in the magazine.
Gas operated
Gases generated by burning powder are tapped off of the barrel (gas port) and channeled back to a piston. The piston pushes the bolt back extracting and ejecting the cartridge case. A recoil spring pushes the bolt forward stripping a cartridge from the magazine pushing it into the chamber and locking the bolt. System used in highpower rifles, shotguns and very few pistols.
Blow back
Rely on the weight of the breech block and recoil spring to keep the action closed until the pressure inside the barrel drops to a safe level. Used in rimfire rifles or carbines which used centerfire pistol cartridges.
Recoil Operated
At the moment of firing the barrel and the bolt or slide are locked so that they travel backward together. At some point the bolt or slide disengages from barrel and continues to travel backward. The action opens and ejects the shell. The recoil spring then pushes the bolt forward feeding a cartridge into the chamber from the magazine. This type of action is used primarily in pistols and a few shotguns, rarely high-power rifles. For a short time after World War II, the Johnson Automatic rifle was sold as a hunting rifle but it never achieved widespread popularity.
Manually Operated Repeater Actions
Bolt Action
There are two main types of bolt action rifles, turn bolt and straight pull.
Rifles with turn bolts require that the bolt handle to be pulled up to rotate the locking lugs from the recesses in the receiver.
The bolt is then drawn back to eject the fired cartridge. When the bolt is pushed forward, a cartridge is stripped from the magazine and pushed it into the chamber.
The bolt handle is then pushed down to lock the action and the rifle is ready to fire.
With the straight pull action, once the bolt handle starts back, the mechanism in the bolt causes the locking lugs on the bolt to rotate out of the recesses. As the bolt is pulled farther back, it extracts the cartridge case from the chamber and ejects it. When the bolt is pushed forward, it strips cartridge from the magazine and pushes it into the chamber. At the end of the bolts travel, the mechanism in the bolt turns the locking lugs into the recesses in the receiver, locking the action.
Straight pull bolt action rifles can be operated slightly faster than a turnbolt but they do have several drawbacks. This most critical from a military standpoint is that they are prone to jamming when dirty and leverage to extract a stuck case is lacking.
Lever Action Rifles
After the trigger is pulled, the lever is pulled down and forward, ejecting the spent shell casing and recocking the action. The magazine spring pushes the cartridge toward the cartridge lifter. When the lever is brought back the cartridge lifter pushs the cartridge up to the mouth of the chamber and the bolt pushes in the cartridge.
Lever action rifles can be classed into two basic catagories.
The brush gun with a tubular magazine such as the Winchester Model 94 and the high power lever gun using a box magazine with spire point bullets such as the Savage model 99 or the Browning BLR
Savage Model 99 Rifle
Lever action rifles were the first widely available repeating rifles in the United States. During the black powder era they were generally chambered in relatively low powered straight wall cartridges, often purchased with an eye to using them as a hunting rifle and a defensive arm.
Pump or slide action
Somewhat popular in areas where the use of semiautos for hunting is illegal. Used for rimfire rifles as well.
Single Shot Rifle Actions
Falling block
In the falling block action the breach block moves down vertically within the receiver to expose the chamber. It is operated by pivoting the trigger guard down and forward to move the block from the chamber. A good example of this type of firearm is the Martini Henry action.
Rolling Block - Single Shot
Invented by Leonard Geiger in 1863 it is one of the simplest rifle actions invented. Easy to clean and maintain it was popular as a sporting rifle and a military arm in the late 19th Century. Remington Arms was by far the biggest manufacturer of this type of rifle with numerous contracts with many nations throughout the world. Today the rolling block rifles have been superceded by stronger and more modern single shot designs. There are however many thousands of military surplus guns still around and there are still some replica rolling block rifles still being made for the American Market.
To load the Rolling Block
- Pull the hammer to full cock.
- The breech-block in front of the hammer will pivot backward revealing the chamber.
- Insert a cartridge in the chamber and close the breech block. The gun is then ready to fire.
- When the trigger is pulled the hammer strikes the firing pin while also camming the breech-block into place.
- The hammer can then be cocked again, the breech block pulled back and the fired cartridge case pulled out.
Though the rolling block action has been used primarily for rifles, some pistols were also made using the design. One such pistol was the 1871 Remington rolling block pistol used by the United States Navy which used a 50 caliber rimfire cartridge.
Trap door
Single shot action in which the breach block pivots up and forward to expose the chamber.
About Rifling
- The rifle pitch is expressed in the U.S. as 1 turn in however many inches.
- The optimal rifle pitch for a given caliber will vary based on the load selection. Faster twist is used to stabilize longer heavier bullets.
- In high power rifles; 1 in 14 inches is a slow twist used in rifles firing bullets with a low sectional density with a high muzzle velocity such as the 22-250.
1 in 7 is a fast twist used for longer heavier bullets at lower velocities.