Action (Firearm)

In firearms terminology, an action is the physical mechanism that manipulates cartridges and/or seals the breech. The term is also used to describe the method in which cartridges are loaded, locked, and extracted from the mechanism. Actions are generally categorized by the type of mechanism used. A firearm action is technically not present on muzzleloaders as all loading is done by hand. The mechanism that fires a muzzle-loader is called the lock.

Matchlock
The matchlock was the first mechanism, or "lock" invented to facilitate the firing of a hand-held firearm. This design removed the need to lower by hand a lit match into the weapon's flash pan and made it possible to have both hands free to keep a firm grip on the weapon at the moment of firing, and, more importantly, to keep both eyes on the target.

Description
The classic matchlock gun held a burning slow match in a clamp at the end of a small curved lever known as the serpentine. Upon the pulling of a lever (or in later models a trigger) protruding from the bottom of the gun and connected to the serpentine, the clamp dropped down, lowering the smoldering match into the flash pan and igniting the priming powder. The flash from the primer travelled through the touch hole igniting the main charge of propellant in the gun barrel. On release of the lever or trigger, the spring-loaded serpentine would move in reverse to clear the pan. For obvious safety reasons the match would be removed before reloading of the gun. Both ends of the match were usually kept alight in case one end should be accidentally extinguished.

Earlier types had only an "S"-shaped serpentine pinned to the stock either behind or in front of the flash pan (the so-called "serpentine lock"), one end of which was manipulated to bring the match into the pan.

Most matchlock mechanisms mounted the serpentine forward of the flash pan. The serpentine dipped backward, toward the firer, to ignite the priming. This is the reverse of the familiar forward-dipping hammer of the flintlock and later firearms.

Wheellock
A wheellock, wheel-lock or wheel lock, is a friction-wheel mechanism to cause a spark for firing a firearm. It was the next major development in firearms technology after the matchlock and the first self-igniting firearm. The mechanism is so-called because it uses a rotating steel wheel to provide ignition. It was used alongside the matchlock and was later superseded by the snaplock.

Description
The wheellock works by spinning a spring-loaded steel wheel against a piece of pyrite to generate intense sparks which ignite gunpowder in a pan, which flashes through a small touchhole to ignite the main charge in the firearm's barrel. The pyrite is clamped in vise jaws on a spring-loaded arm (or 'dog') which rests on the pan cover. When the trigger is pulled, the pan cover automatically opens, and the wheel spins as the pyrite is pressed into contact.

A close modern analogy of the wheellock mechanism is the operation of a modern cigarette lighter which spins a toothed steel wheel against a sparking material to ignite the fuel into a flame. However, the wheellock is used to send the flame to then ignite the charge in the barrel.

A wheellock firearm can be instantly readied and fired even one-handed, in contrast to the then-common matchlock firearms which must have a burning cord of slow-match ready if the gun might be needed, and which demand the operator's full attention and two hands to operate. The wheellock mechanism is complex to make, making it relatively costly.

The "Dog"
The dog is a spring-loaded arm pivoted on the outside of the lock plate. A sparking material, usually a small piece of iron pyrite, is clamped and held by vice-like jaws at the swinging end of the arm. This dog has two possible positions to which it can be pivoted by hand: a "safe" position, in which the dog is pushed towards the muzzle of the firearm, and an "operating" position, where the dog is pulled towards the operator so that the pyrite in its jaws can engage either the top of the pan cover (see below), or (in the absence of the pan cover) the edge of a steel wheel bearing longitudinal grooves around its circumference. Flint is not suitable as a sparking material in the wheellock because it is too hard and would quickly wear away the wheel grooves.

The Wheel
The upper segment of this grooved wheel, made of hardened steel, projects through a slot cut to its precise dimensions in the base of the priming pan. This wheel is grooved on its outside circumference with three or more V-shaped grooves with transverse cuts at intervals to provide a friction surface for the iron pyrites. The wheel is fixed to a shaft, one end of which projects outside the lockplate. This outside projection is of square section to permit a spanner (wrench) to be engaged for subsequent tensioning of the lock. The other end of the shaft fits through a hole in the lockplate, and on this end is forged a cam, or eccentric. One end of a short, robust chain (made of three or four flat, parallel links like a short piece of bicycle chain) is fixed to the cam, while the other end of the chain is held in a groove at the end of the longer branch of a large heavy V-spring which is generally retained by a screw and a headed bracket through upstands inside the lockplate.

The Pan
As in all muzzle-loading firearms (prior to the introduction of the percussion cap), the pan transmits the fire to the main charge of gunpowder inside the breech of the barrel, via a small hole (or "vent") in the side of the breech, that gives on to the pan. The priming pan of all wheellocks is provided with a sliding cover that has two purposes, the first of which is to contain the priming powder and afford it some protection from the elements (the second is examined below, under 'Operation'). The pan cover may be slid open and closed by hand, but it is also attached to an arm inside the lock plate, which is acted upon by the eccentric on the shaft of the wheel.

The Sear or Trigger Mechanism
The trigger engages one arm of a "z"-shaped sear pivoting in its centre between two upstanding brackets riveted or brazed to the inside of the lockplate. The other arm of the sear passes through a hole in the lockplate, and engages in a blind hole on the inner side of the wheel, thus effectively locking it and preventing any rotation but only because of a secondary sear or wedge that is pressed under the rear arm of the sear - that is between the lockplate and the sear- when the forward part of it engages into the recess in the wheel. When the trigger is pulled, this secondary lever is withdrawn from its position and the strong pull of the mainspring pushes the unsupported main sear back into the lock and the wheel is free to rotate. This mechanism may seem overconstructed, but it prevents the trigger mechanism from working against the very powerful mainspring as it is the case with all vertical acting sears in flint and percussion locks or even modern firearms that still have cocks (revolvers).

Preparing To Fire
First, the dog is rotated forward to the "safe" position, and the priming pan pushed open (if it is not already so). After loading a powder charge and ball through the muzzle in the usual way, the operator takes his "spanner", slips it on to the square section of the wheel shaft, and turns it until a click is heard (about one half to three-quarters of a revolution), and the wheel is felt to lock in place, whereupon the spanner is withdrawn. What occurs is that when the wheel is turned, the mainspring is tensioned via the chain, which is wound partially around the shaft. The click is the sound of one end of the sear engaging in the blind hole on the inside of the wheel, as described above, thus immobilising it.

The pan is then primed with powder, and the pan cover pulled shut. Finally the dog is pulled back so that the pyrite in its jaws is resting on the top of the pan cover, under some pressure from the spring at the toe of its arm.

Operation
On pulling the trigger of a wheellock firearm, the sear effects a slight rotation as described above. The end of the sear arm (that has hitherto locked the wheel and prevented it from turning) is disengaged, leaving the wheel free to turn under the tension of the mainspring. There is a subtlety here that is of vital importance: the "hole" in the side of the wheel, into which the sear engages, is not a parallel-sided shaft. If it were, then under the tremendous tension of the mainspring, it would require a huge force on the trigger to disengage the sear. Nor is the tip of the sear arm cylindrical, which would have a similar effect. Rather, the "hole" is a depression in the wheel (like a small crater), and the sear has a rounded end: the wheel is locked by reason of lateral force on the shaft of the wheel rather than vertical force on the sear.

As soon as the wheel is released by the sear, the longer arm of the mainspring pulls the chain engaged in it. The other end of the chain being fixed to the cam on the wheel shaft, the latter rotates at high speed, whilst the rotating cam pushes forward the arm to which the pan cover is attached, thus causing the pan cover to slide forward towards the muzzle of the piece, and the pyrites to fall (under tension of the dog spring) on to the now rotating wheel. This is the second purpose of a sliding pan cover: were the pyrites to engage a stationary wheel, it would almost certainly jam the mechanism: but the built-in delay allows the pyrites to slip off the sliding pan-cover on to an already rotating wheel.

The fast rotation of the wheel against the pyrites produces white-hot sparks that ignite the powder in the pan, which is transferred to the main charge in the breech of the barrel via the vent, and the gun discharges.

The wheellock took around a minute to load, prepare and fire. Many contemporary illustrations of a wheellock pistol in action show the gun held at a 90 degree angle rather than vertically: this was to ensure that the priming powder in the pan lay against the vent in the barrel, and avoided a 'flash in the pan' or misfire (this was not the case for the flintlock, where the sparks had to fall vertically a certain distance on to the pan).

Snaplock
A Snaplock is a particular type of mechanism for firing a gun (also, a gun fired by such a mechanism).

A snaplock ignites the (usually muzzleloading) weapon's propellant by means of sparks produced when a spring-powered cock strikes a flint down on to a piece of hardened steel. The snaplock is therefore similar to the snaphaunce (sometimes classed as an advanced type of snaplock) and the later flintlock (see below).

In all snaplocks, the flint is held in a clamp at the end of a bent lever called the cock. When the gun is "cocked", the cock is held back, against the pressure of a spring, by a catch which is part of the trigger mechanism. When the trigger is pulled, the catch is released and the spring moves the cock rapidly forwards. The flint strikes a curved plate of hardened steel, called the "steel". The flint strikes from the steel a shower of white hot steel shavings (sparks) which fall towards the priming powder held in the flash pan. The flash from the pan's ignited primer travels (unless there is only a "flash in the pan") through the touch hole into the firing chamber at the rear of the barrel, and ignites the main charge of gunpowder.

Before the weapon is fired, the pan has a closed cover: the mechanism for opening this cover (i.e. manual or automatic) can affect whether the weapon is classed as a snaplock.

Safety
Snaplocks as a class did not have safety devices, but individual models could be prevented from inadvertent firing by different mechanisms
 * In the early models with a manual pan cover, the steel could be swung out of the path of the flint until just before firing., also, a closed pan cover would not allow the primer to ignite and could help keep the primer dry in misty conditions.
 * On some models, an external hook attached to the lock plate could engage the tip of the "cocked" cock to prevent it from moving forwards.

Snaphance
A Snaphance or Snaphaunce is a particular type of mechanism for firing a gun or a gun using that mechanism. The name is Dutch in origin but the mechanism can not be attributed to the Netherlands with certainty. It is the mechanical progression of the wheel-lock firing mechanism and the predecessor of the flintlock firing mechanism. It fires from a flint struck against a striker plate above a steel pan to ignite the priming powder which fires the gun.

Design
Like the earlier snaplock and later flintlock, the snaphance drives a flint onto a steel to create a shower of sparks to ignite the main charge (propellant).

The flint is held in a clamp at the end of a bent lever called the cock. Upon pulling the trigger, this moves forward under the pressure of a strong spring and strikes a curved plate of hardened steel (called simply the steel, or in 17th century English dialect the frizzen) to produce a shower of sparks (actually white-hot steel shavings). These fall into a flash pan holding priming powder. The flash from the pan travels through the touch hole to cause the main charge of gunpowder to explode. The steel is at the end of an arm that can be moved independently of the pan cover.

Flintlock
Flintlock is the general term for any firearm based on the flintlock mechanism. The term may also apply to the mechanism itself. Introduced at the beginning of the 17th century, the flintlock rapidly replaced earlier firearm-ignition technologies, such as the doglock, matchlock, and wheellock mechanisms. It continued to be in common use for over two centuries, replaced by percussion cap and, later, cartridge-based systems in the early-to-mid 19th century. Although long superseded by modern firearms, flintlock weapons enjoy continuing popularity with black-powder shooting enthusiasts.

Method Of Operation
The gun is now in a "primed and loaded" state, and this is how it would typically be carried while hunting or if going into battle.
 * A cock tightly holding a sharp piece of flint is rotated to half-cock, where the sear falls into a safety notch on the tumbler, preventing an accidental discharge.
 * The operator loads the gun, usually from the muzzle end, with black powder from a powder flask, followed by lead shot, a round lead ball, usually wrapped in a piece of paper or a cloth patch, all rammed down with a ramrod that is usually stored on the underside of the barrel. Wadding between the charge and the ball was often used in earlier guns.
 * The flash pan is primed with a small amount of very finely ground gunpowder, and the flash pan lid or frizzen is closed.

To Fire:
 * The cock is further rotated from half-cock to full-cock, releasing the safety lock on the cock.
 * The gun is leveled and the trigger is pulled, releasing the cock holding the flint.
 * The flint strikes the frizzen, a piece of steel on the priming pan lid, opening it and exposing the priming powder.
 * The contact between flint and frizzen produces a shower of sparks (burning pieces of the metal) that is directed into the gunpowder in the flashpan.
 * The powder ignites, and the flash passes through a small hole in the barrel (called a vent or touchhole) that leads to the combustion chamber where it ignites the main powder charge, and the gun discharges.
 * The powder charge and ball were instantly available to the soldier inside this small paper envelope. *To load a flintlock weapon using a paper cartridge, a soldier would;
 * move the cock to the half-cock position;
 * tear the cartridge open with his teeth;
 * fill the flashpan half-full with powder, directing it toward the vent;
 * close the frizzen to keep the priming charge in the pan;
 * pour the rest of the powder down the muzzle and stuff the cartridge in after it;
 * take out the ramrod and ram the ball and cartridge all the way to the breech;
 * replace the ramrod;
 * shoulder the weapon.

The weapon can then be cocked and fired.

Caplock Mechanism
The caplock mechanism or percussion lock was the successor of the flintlock mechanism in firearm technology, and used a percussion cap struck by the hammer to set off the main charge, rather than using a piece of flint to strike a steel frizzen.

The rudimentary percussion system was developed as a solution to the problem that birds would startle when smoke puffed from the powder pan of his flintlock shotgun, giving them sufficient warning to escape the shot. The invention of a fulminate-primed firing mechanism deprived the birds of their early warning system, both by avoiding the initial puff of smoke from the flintlock powder pan, as well as shortening the interval between the trigger pull and the shot leaving the muzzle.

The caplock offered many improvements over the flintlock. The caplock was easier to load, more resistant to weather, and was much more reliable than the flintlock. Many older flintlock weapons were later converted into caplocks so that they could take advantage of this increased reliability.

The caplock mechanism consists of a hammer, similar to the hammer used in a flintlock, and a nipple (sometimes referred to as a "cone"), which holds a small percussion cap. The nipple contains a tube which goes into the barrel. The percussion cap contains a chemical compound called mercuric fulminate or fulminate of mercury, whose chemical formula is Hg(ONC)2. It is made from mercury, nitric acid and alcohol. When the trigger releases the hammer, it strikes the cap, causing the mercuric fulminate to explode. The flames from this explosion travel down the tube in the nipple and enter the barrel, where they ignite the main powder charge.

Bolt Action
Bolt action is a type of firearm action in which the weapon's bolt is operated manually by the opening and closing of the breech (barrel) with a small handle, most commonly placed on the right-hand side of the weapon (for right-handed users). As the handle is operated, the bolt is unlocked, the breech is opened, the spent cartridge case is withdrawn and ejected, the firing pin is cocked (this occurs either on the opening or closing of the bolt, depending on design), and finally a new round/cartridge (if available) is placed into the breech and the bolt closed. Bolt action firearms are most often rifles, but there are some bolt-action shotguns and a few handguns as well.

In military and law enforcement use, the bolt action has been mostly replaced by semi-automatic and selective fire weapons, though the bolt action remains the dominant design in dedicated sniper rifles. Bolt action firearms are still very popular for hunting and target shooting. Compared to most other manually operated firearm actions, it offers an excellent balance of strength (allowing powerful cartridge chamberings), ruggedness, reliability, and potential accuracy, all with light weight and much lower cost than self-loading firearms, and can also be disassembled and re-assembled much faster due to fewer moving parts. The major disadvantage is a slightly lower practical rate of fire than other manual repeating firearms, such as lever-action and pump-action, and a far lower practical rate of fire than semi-automatic weapons, but this is not a very important factor in many types of hunting, target shooting, and other precision-based shooting uses.

Operating The Bolt
Typically, the bolt consists of a tube of metal inside of which the firing mechanism is housed, and which has at the front or rear of the tube several metal knobs, or "lugs", which serve to lock the bolt in place. The operation can be done via a rotating bolt, a lever, cam-action, locking piece, or a number of systems. Straight-pull designs have seen a great deal of use, though manual turn-bolt designs are what is most commonly thought of in reference to a bolt-action design due to the type ubiquity. As a result the bolt-action term is often reserved for more modern types of rotating bolt-designs when talking about a specific weapon's type of action, however both straight-pull and rotating bolt rifles are types of bolt-action rifles. Lever-action and pump-action weapons must still operate the bolt, but they are usually grouped separately from bolt-actions that are operated by a handle directly attached to a rotating bolt. he most common locking method is a rotating bolt with two lugs on the bolt head.

Loading
Most bolt-action firearms are fed by an internal magazine loaded by hand, by en bloc, or stripper clips, though a number of designs have had a detachable magazine or independent magazine, or even no magazine at all, thus requiring that each round be independently loaded. Generally, the magazine capacity is limited to between two and ten rounds, as it can permit the magazine to be flush with the bottom of the rifle, reduce the weight, or prevent mud and dirt from entering. A number of bolt-actions have a tube magazine, such as along the length of the barrel. In weapons other than large rifles, such as pistols and cannons, there were some manually operated breech loading weapons.

Benefits & Drawbacks
Bolt-action firearms can theoretically achieve higher muzzle velocity and therefore have more accuracy than semi-automatic rifles because of the way the barrel is sealed. In a semiautomatic rifle, some of the energy from the charge is directed towards ejecting the spent shell and loading a new cartridge into the chamber. In a bolt action, the shooter performs this action by manually operating the bolt, allowing the chamber to be better sealed during firing, so that much more of the energy from the expanding gas can be directed forward. However, numerous other factors related to design and ammunition affect reliability and accuracy, and well designed modern semi-automatic rifles can be exceptionally accurate. Because of the combination of relatively light weight, reliability, high potential accuracy and lower cost, the bolt action is still the design of choice for many hunters, target shooters and snipers.

The bolt action's locking lugs are normally at the front of the breech (some designs have additional "safety lugs" at the rear) and this increases potential accuracy relative to a design which locks the breech at the rear, such as a lever action. Also, a bolt action's only moving parts when firing are the pin and spring. Since it has fewer moving parts and a short lock time, it has less of a chance of being thrown off target and/or malfunctioning.

Because the spent cartridge is removed by manual action rather than automatically ejected, it can help a sniper remain hidden. Because the cartridge is not visibly flung into the air and onto the ground, a bolt action may be less likely to reveal a sniper's position. Also, the cartridge can be removed when most prudent, allowing the sniper to remain still until reloading is tactically feasible. Bolt actions are also easier to operate from a prone position than other manually repeating mechanisms and work well with box magazines which are easier to fill and maintain than tubular magazines.

The integral strength of the design means very powerful magnum cartridges can be chambered without significantly increasing the size or weight of the weapon. For example, some of the most powerful elephant rifles are in the same weight range (7-10 lbs.) as a typical deer rifle, while delivering several times the kinetic energy to the target. The recoil of these weapons, however, is correspondingly severe. By contrast, the operating mechanism of a semi-automatic weapon must increase in mass and weight as the cartridge it fires increases in power. This means that semi-automatic rifles firing magnum cartridges tend to be relatively heavy and impractical for many types of hunting.

The bolt action requires four distinct movement and is therefore generally the slower than other major manual repeating mechanisms, such as lever and pump action, which generally require two, although straight-pull bolt actions also require only two distinct movements. Also, the trigger hand must leave the gun and regrip the weapon after each shot, usually resulting in the shooter having to realign his sight and reacquire the target for every shot. It is also not ambidextrous, and left-handed models tend to be more expensive.

Lever-Action
Lever-action is a type of firearm action which uses a lever located around the trigger guard area (often including the trigger guard itself) to load fresh cartridges into the chamber of the barrel when the lever is worked. This contrasts to bolt action, semi-automatic, or selective fire weapons. Most lever-action firearms are rifles, but lever-action shotguns and a few pistols have also been made. While the term lever-action generally implies a repeating firearm, it is also sometimes (and incorrectly) applied to a variety of single-shot, or falling-block actions that use a lever for cycling.

Advantages and disadvantages
While lever-action rifles were (and are) popular with hunters and sporting shooters, they were not widely accepted by the military. One significant reason for this was that it is harder to fire a lever-action from the prone position (compared to a straight-pull or rotating-bolt bolt-action rifle), and while nominally possessing a greater rate of fire (contemporary Winchester advertisements claimed their rifles could fire 2 shots a second) than bolt-action rifles, lever-action firearms are also generally fed from a tubular magazine, which limits the ammunition that can be used in them. Pointed center fire Spitzer bullets, for example, can cause explosions in a tubular magazine, as the point of each cartridge's projectile rests on the primer of the next cartridge in the magazine (elastomer-tipped Hornady LEVERevolution ammunition overcomes this problem). The tubular magazine may also have a negative impact on the harmonics of the barrel, which limits the theoretical accuracy of the rifle. A tubular magazine under the barrel also pushes the center of gravity forward, which alters the balance of the rifle in ways that are undesirable to some shooters. However there are some lever rifles, such as the Winchester Model 1895 which saw service with the Russian Army in World War I, that use a box magazine. Furthermore, many of the newer lever action rifles are capable of shooting groups smaller than 1 minute of angle, making them closer to the accuracy of most modern bolt-action rifles than in the past.

Due to the higher rate of fire and shorter overall length than most bolt-action rifles, lever actions have remained popular to this day for sporting use, especially short- and medium-range hunting in forests, scrub, or bushland. Lever-action firearms have also been used in some quantity by prison guards in the United States, as well as by wildlife authorities/game wardens in many parts of the world.

An additional advantage over typical bolt-action rifles is the lack of handedness: lever-actions like pump-actions are frequently recommended as ambidextrous in sporting guidebooks.

Pump-Action
A pump-action rifle or shotgun is one in which the handgrip can be pumped back and forth in order to eject a spent round of ammunition and to chamber a fresh one. 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.

Advantages
The cycling time of a pump-action is quite short. 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.

An advantage of the pump-action over the bolt-action is its ease of use by both left- and right-handed users: like lever-actions, pump-actions are frequently recommended as ambidextrous in sporting guidebooks. However, most are not truly ambidextrous, as the spent casing is ejected out the side in most designs.

Disadvantages
Like most lever-action rifles, most pump-action shotguns and rifles do not use a detachable magazine. This makes for slow reloading, as the cartridges have to be inserted individually into the firearm. Some pump action shotguns and rifles, use detachable box magazines.

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. 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.

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 are considered more reliable 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.

Revolver
A revolver is a repeating firearm that has a revolving cylinder containing multiple chambers and at least one barrel for firing. The term "revolver" refers to a handgun, but other weapons may also have a revolving chamber. These include some models of grenade launchers, shotguns, and rifles.

Though the original name was "revolving gun", the short-hand "revolver" is universally used. (Cannons using this mechanism are known as revolver cannons.) Nearly all early revolvers and many modern ones have six chambers in the cylinder, giving rise to the slang term "six-shooter"; however, revolvers with 3 to 24 chambers have been made, with most modern revolvers having 5 or 6 chambers.

The revolver allows the user to fire multiple rounds without reloading. Each time the user cocks the hammer, the cylinder revolves to align the next chamber and round with the hammer and barrel, which gives this type of firearm its name. In a single-action revolver, the user pulls the hammer back with his free hand or thumb; the trigger pull only releases the hammer. In a double-action revolver, pulling the trigger moves the hammer back, then releases it.

Design
A revolver works by having several firing chambers arranged in a circle in a cylindrical block that are brought into alignment with the firing mechanism and barrel one at a time. In contrast, other repeating firearms, such as lever-action, pump-action, and semi-automatic, have a single firing chamber and a mechanism to load and extract cartridges into it.

A single-action revolver requires the hammer to be pulled back by hand before each shot, which also revolves the cylinder. This leaves the trigger with just one "single action" left to perform - releasing the hammer to fire the shot - so the force and distance required to pull the trigger can be minimal. In contrast, with a self-cocking revolver, one long squeeze of the trigger pulls back the hammer and revolves the cylinder, then finally fires the shot. They can generally be fired faster than a single-action, but with reduced accuracy in the hands of most shooters.

Most modern revolvers are "traditional double-action", which means they may operate either in single-action or self-cocking mode. The accepted meaning of "double-action" has, confusingly, come to be the same as "self-cocking", so modern revolvers that cannot be pre-cocked are called "double-action-only". These are intended for concealed carry, because the hammer of a traditional design is prone to snagging on clothes when drawn. Most revolvers do not come with accessory rails, which are used for mounting lights and lasers.

Most commonly, such revolvers have a 5 or 6 shot capacity, hence the common names of "six-gun" or "six-shooter". However, some revolvers have a 7 to 10 shot capacity, often depending on the caliber, and at least one revolver has a 12 shot capacity. Each chamber has to be reloaded manually, which makes reloading a revolver a much slower procedure than reloading a semi-automatic pistol.

Compared to autoloading handguns, a revolver is often much simpler to operate and may have greater reliability. For example, should a semiautomatic pistol fail to fire, clearing the chamber requires manually cycling the action to remove the errant round, as cycling the action normally depends on the energy of a cartridge firing. With a revolver, this is not necessary as none of the energy for cycling the revolver comes from the firing of the cartridge, but is supplied by the user either through cocking the hammer or, in a double action design, by just squeezing the trigger. Another significant advantage of revolvers is superior ergonomics, particularly for users with small hands. A revolver's grip does not hold a magazine, and it can be designed or customized much more than the grip of a typical semi-automatic. Partially because of these reasons, revolvers still hold significant market share as concealed carry and home-defense weapons.

A revolver can be kept loaded and ready to fire without fatiguing any springs and is not very dependent on lubrication for proper firing. Additionally, in the case of double-action-only revolvers there is no risk of accidental discharge from dropping alone, as the hammer is cocked by the trigger pull. However, the revolver's clockwork-like internal parts are relatively delicate and can become misaligned after a severe impact, and its revolving cylinder can become jammed by excessive dirt or debris.

Revolver technology lives on in other weapons used by the military. Some autocannons and grenade launchers use mechanisms similar to revolvers, and some riot shotguns use spring-loaded cylinders holding up to 12 rounds. In addition to serving as backup guns, revolvers still fill the specialized niche role as a shield gun; law enforcement personnel using a "bulletproof" ballistic shield (Gun shield) sometimes opt for a revolver instead of a self-loading pistol, because the slide of a pistol may strike the front of the shield when fired. Revolvers do not suffer from this disadvantage. A second revolver may be secured behind the shield to provide a quick means of continuity of fire. Many police also still use revolvers as their duty weapon due to their relative mechanical simplicity and user friendliness.

Blowback
What is common to all blowback systems is that the cartridge case must move under the direct action of the powder pressure, therefore any gun in which the bolt is not rigidly locked and permitted to move while there remains powder pressure in the chamber will undergo a degree of blowback action. The energy from the expansion of gases on firing appears in the form of kinetic energy transmitted to the bolt mechanism, which is controlled and used to operate the firearm's operation cycle. The extent to which blowback is employed largely depends on the manner used to control the movement of the bolt and the proportion of energy drawn from other systems of operation. How the movement of the bolt is controlled is where blowback systems differ. Blowback operation is most often divided into three categories, all using residual pressure to complete the cycle of operation: simple blowback, advanced primer ignition and delayed blowback or retarded blowback.

Recoil
Recoil operation is an operating mechanism used in locked-breech, autoloading firearms. As the name implies, these actions use the force of recoil to provide energy to cycle the action. Other operating systems are blow forward operated, blowback operated, gas operated, and chain.

The same forces that cause the ejecta of a firearm (the projectile(s), propellant gas, wad, sabot, etc.) to move down the barrel also cause all or a portion of the firearm to move in the opposite direction. The result is required by the conservation of momentum and is expressed in the formula:
 * Ejecta momentum = Recoiling momentum
 * which by the definition of momentum is calculated by:
 * Ejecta mass × ejecta velocity = recoiling mass × recoil velocity

In non-recoil-operated firearms, it is generally the entire firearm that recoils. However, in recoil-operated firearms, only a portion of the firearm recoils while inertia holds another portion motionless relative to a mass such as the ground, a ship's gun mount, or a human holding the firearm. The moving and the motionless masses are coupled by a spring that absorbs the recoil energy as it is compressed by the movement and then expands providing energy for the rest of the operating cycle.

Since there is a minimum momentum required to operate a recoil-operated firearm's action, the cartridge must generate sufficient recoil to provide that momentum. Therefore, recoil-operated firearms work best with a cartridge that yields a momentum approximately equal to that for which the mechanism was optimized. Changes in caliber or drastic changes in bullet weight and/or velocity require modifications to spring weight or slide mass to compensate.

Long-Stroke Piston
With a long-stroke system, the piston is mechanically fixed to the bolt group and moves through the entire operating cycle. The primary advantage of the long-stroke system, beyond design simplicity and robustness, is that the mass of the piston rod adds to the momentum of the bolt carrier enabling more positive extraction, ejection, chambering, and locking. Also, as the gas is not directed back into the chamber, the weapon stays cleaner longer thus reducing the likelihood of a malfunction. The primary disadvantage to this system is the disruption of the point of aim due to the center of mass changing during the action cycle, and energetic and abrupt stops at the beginning and end of bolt carrier travel. Also, due to the greater mass of moving parts, more gas is required to operate the system.

Direct Impingement
The direct impingement (DI) method of operation vents gas through a tube to the working parts of a rifle where they directly impinge on the bolt carrier. Rifles that use this system include the Swedish Ljungman Ag m/42, U.S. M16 and French MAS-49. This system has the advantage of having the absolute minimum of recoiling action parts, resulting in the minimum possible weapon disturbance due to balance shifting during the action cycle as well as reducing overall weapon weight. It has the disadvantage of the propellant gas (and the accompanying fouling) being blown directly into the action parts. DI operation increases the amount of heat that is deposited in the receiver while firing of the M16 and causing essential lubricant to be "burned off". Lack of proper lubrication is the most common source of weapon stoppages or jams. The bolt, extractor, ejector, pins, and springs are heated by this high-temperature gas. These combined factors reduce service life of these parts, reliability, and mean time between failures.

Short-Stroke Piston
With a short-stroke or tappet system, the piston moves separately from the bolt group. It may directly push the bolt group parts as in the M1 carbine or operate through a connecting rod or assembly as in the Armalite AR-18 or the SKS. In either case, the energy is imparted in a short, violent push and the motion of the gas piston is then arrested allowing the bolt carrier assembly to continue through the operating cycle through kinetic energy. This has the advantage of reducing the total mass of recoiling parts compared to the long-stroke piston. This, in turn, enables better control of the weapon due to less mass needing to be stopped at either end of the bolt carrier travel.

Electrical Motor
In Electrical motor driven firearms, the movement of the firing pin, and the ejection functions are both controlled by an electric motor thereby drastically increasing the rate of fire.

Electromagnetic Motor
In Electromagnetic motor driven firearms, the operation of the weapon is nearly identical to electrically driven firearms, but there are now physical linkages to get jammed, and thereby drastically increasing the reliability of the weapon.