Rifle actions can be very roughly grouped into single shot, bolt action, self-loading and pump action.

Single shot. In single- shot weapons, the barrel can be hinged to the frame, allowing the barrel to be dropped down for loading and unloading, or can have some form of breech block which either swings out, pulls back or slides down to expose the breech end of the barrel.

Bolt action. In bolt-action weapons, a turning bolt slides in an extension to the barrel, which is basically the same system as in a turn bolt used to lock a door. Pushing the bolt forward brings the bolt face into battery with the breech end of the barrel and cocks the striker (or firing pin). Turning the bolt then locks it into place via bolt lugs engaging with slots in the barrel extension. Other bolt-action weapons cock the striker on the opening of the bolt (Figure 1.16).

Straight-pull bolt actions also exist in which the rotary motion required to turn the bolt locking lugs into their recesses is applied by studs on the bolt which slide in spiral grooves cut into the barrel extension.

Bolt-action weapons are generally magazine fed, either by a tubular magazine under the barrel, through the butt stock or via a box magazine under the

Self-loading rifles. Self-loading rifles are, with the exception of the lowest power weapons, of the locked-breech type. These are generally very similar to those used in locked-breech pistols, but of a much stronger design to cope with the higher pressures involved (Figure 1.17).

There are basically two types of self-loading rifle action:

• Short recoil, in which the bolt and breech block are only locked together for about 0.75" of rearward travel before unlocking. It then operates as a normal self-loading pistol.

• Long recoil, in which the barrel and breech block are locked together for the full distance of the recoil stroke. After reaching the end of its travel, the barrel is then unlocked and pushed forward by spring action ejecting the spent cartridge during its forward motion. When the barrel is fully forward, the breech bolt.

Receiver bridge

Rear sight

Front sight




Bolt handle rinn




Bolt handle rinn

Rifle 458 Part Name



Figure 1.16 Bolt-action rifle.





Figure 1.16 Bolt-action rifle.

M16 Self Loading Carbine Parts
Figure 1.17 Self-loading rifle.
Rifle Parts Names

Figure 1.18 Pump-action rifle


Figure 1.18 Pump-action rifle block begins its forward motion reloading a fresh cartridge into the chamber and cocking the action.

Pump action. In pump - action weapons (sometimes also referred to as slide action), the breech block is attached, via operating rods, to a moveable fore-end. On pulling back the fore-end, the mechanism locking the breech block to the barrel is released. By pulling the fore - end to the rearmost extent of its travel then pushing it forward, the empty cartridge case is ejected, a fresh round is loaded into the chamber and the action is cocked (Figure 1.18).

1.2.3 Shotguns

Shotgun actions are basically the same as those found in rifles, with single/ double-shot weapons with barrels hinged to the frame for loading/unloading, bolt action, self-loading and pump-action. Barrels can be either positioned one on top of the other, over and under or 'superposed' or 'side by side ' .

In the smaller calibres, that is, 0.22", 9-mm and 0.410", double-barrelled shot pistols are occasionally encountered.

Shotgun/rifle combinations are popular in Europe and can consist of one shotgun barrel and one rifle barrel (vierling), two shotgun barrels with one rifle barrel (drilling) or two rifle barrels and one shotgun barrel (also called a drilling).

1.2.4 Sub-machine guns (smg)

Sub-machine guns are really outside the scope of this book, but a brief description is relevant. These are fully automatic weapons generally chambered for pistol calibre ammunition. The simplest type of action encountered is a simple blowback. To overcome the problems of the cartridge exiting the chamber before the pressures have dropped to safe levels, a very heavy reciprocating bolt and a large spring are employed to delay the cartridge extraction. The classic example of this type of action is the Sten gun used by the British forces in World War II (WWII). Whilst this is an extremely simple, cheap to manufacture and reliable action, it does tend to be rather heavy. More modern weapons are equipped with some form of delayed blowback action of the type used in self-loading pistols and rifle actions, for example, the Uzi. Whilst this does produce a much lighter weapon, it is much more expensive to manufacture and, being more complicated, more prone to malfunction.

1.2.5 Machine guns and heavy machine guns

These are well outside of the scope of this book, but basically, a machine gun is a long-barrelled automatic weapon firing rifle calibre ammunition. A heavy machine gun is very similar to a machine gun, but it is much more sturdily built, often with a water jacket round the barrel to prevent overheating and a consequential rapid rate of wear. Being much heavier, it is generally mounted on a sturdy tripod and is designed for sustained high rates of fire.

1.2.6 Headspace

Headspace is not a subject that comes up in the everyday examination of firearms cases. It is, however, a subject that one should be aware of and be able to answer questions upon if asked.

In firearms terms, the headspace is the distance measured from the part of the chamber that stops forward motion of the cartridge (the datum line) to the face of the bolt.

Figure 1.19 Over and under shotgun.
Single Barrel Shotgun 410 Silencer
Figure 1.20 Headspace measurement for various cartridge types.

With cartridges having a rim, the headspace is measured from the back face of the barrel to the face of the breech.

With rimless cases, it is measured from either the mouth of the case (if a straight-walled case) or from a datum point on the shoulder of the case (Figure 1.20).

Headspace is measured using a precision gauge cut to the dimensions required.

Headspace gauges generally come in three sizes: a 'go' gauge on which the action will close and lock up, a 'no-go' gauge on which the action can only be partially closed or closed only with some effort and a 'field' gauge on which the action should not be able to be closed on (Figure 1.21).

Excessive headspace allows movement of the case during firing which can cause case stretching, case separation (ruptured case) and gas leakage.

When the powder is ignited, the base of the cartridge can move back whilst the sides of the case stick to the walls of the chamber. As a result, the case can

Figure 1.21 Rimless cartridge headspace gauge.

Figure 1.21 Rimless cartridge headspace gauge.

separate and rupture. If the bolt and receiver are not strong enough to contain and vent the blast, serious damage can be caused to both the firer and the firearm itself.

Some military firearms are designed to handle a problem like case rupture. The ported holes on the side of Mauser bolts are an example of a design to vent off gases that may be inadvertently sent through the bolt to the rear of the firearm.

Insufficient headspace prevents the closing of the bolt and possibly the complete chambering of the cartridge. If the bolt is forced closed, this can cause the bullet to be compressed further into the neck of the cartridge' s case. This will lead to over-pressure conditions when the cartridge is fired and may cause very similar results to that caused by excessive headspace; the case may rupture sending very hot, high-pressure gases through the rear of the receiver.

1.2.7 Muzzle attachments

Rifles, pistols and revolvers can be found with six types of muzzle attachment. These are:

1. sound suppressors (often wrongly called silencers);

2. recoil reducers, also referred to as compensators;

3. flash hiders;

4. muzzle counter weights (mainly for target weapons);

5. grenade dischargers;

6. recoil boosters.

Shotguns can also be fitted with all of the above, although they are most likely to be found with either fixed or adjustable chokes or a recoil reducer.

1.2.8 Sound suppressors

There are four distinct components that together make up the noise we perceive as a gunshot. In order of loudness, these are:

Gun barrel


Figure 1.22 Typical silencer construction.

1. pressure wave from rapidly expanding propellant gases;

2. supersonic crack of bullet as it passes through the sound barrier;

3. mechanical action noise;

4. flight noise.

The pressure wave. This is produced by the rapidly expanding propellant gases and is, generally, the only noise component that a suppressor can reduce.

Exceptions include those weapons where the silencer is integral to the barrel and is designed to bleed off gases before the bullet reaches supersonic speed. Examples would include the H&K MP5SD and High Standard Model HD.

As the expanding gases exit the barrel of an unsuppressed barrel, they rapidly expand causing a loud bang which is basically due to the gases exceeding the speed of sound (approximately 1100 ft/s). The suppressor reduces this noise by the slow release, through expansion and turbulence, of high-pressure propellant gases to the point where they no longer exceed this velocity.

The basic design of a sound suppressor consists of an expansion chamber (in Figure 1.22 this wraps back around the barrel to decrease the length of the suppressor) and a series of baffles to further reduce the speed of the emerging gases.

Suppressors can either be an integral part of the weapon or a muzzle attachment to be screwed on, attached via a bayonet type fitment or with grub screws.

Integral suppressors can be designed that the gases are bled off (ported) into the expansion chamber before the bullet reaches supersonic speeds. Example of weapons with an integral suppressor would include the High Standard HD 0.22" slp and the H&K MP5SD 9 mm PB smg. In these weapons, bleeding the gases off early reduces the final velocity of the bullet to below that of sound thus allowing standard ammunition to be used rather than a reduced loading.

Most suppressors for supersonic cartridges can realistically be expected to reduce the noise of firing by 18-32 dB depending on the design.

Supersonic crack. This can only be removed by either utilizing subsonic ammunition or via a ported barrel to bleed off propellant gas and thus reduce the velocity of the bullet.

Bullet flight noise. Bullet flight noise is not loud enough to be sensed by the shooter, although they can be distinctly heard if they pass close by a person.

This noise resembles a distinctive high-pitched whirring sound as the bullet flies through the air. Flight noise is too quiet to be heard above the sonic crack.

Mechanical noise. This is caused by the weapon's hammer, firing pin, locking mechanism and so on. This can, to a certain extent, be reduced by the use of single-shot weapons with a cushioned firing pin. The WWII Special Forces Welrod is an example of such a weapon. It was made in 9 mm PB, 0.380 ACP and 0.32 ACP calibres, and was virtually silent in operation.

Sound suppressors also function as flash suppressors and, to a certain extent, recoil reducers.

1.2.9 Recoil reducers

Muzzle brakes and recoil compensators are devices that are fitted to the muzzle of a firearm to redirect propellant gases with the effect of countering both recoil of the gun and unwanted rising of the barrel during rapid fire.

Generally speaking, a muzzle brake is external to the barrel of the firearm, whilst a recoil compensator is typically part of the structure of the barrel proper.

A properly designed muzzle brake can significantly reduce recoil. The actual effectiveness depends to an extent on the cartridge for which the rifle is chambered with claims of up to 60% being made.

Recoil compensators are generally less efficient than muzzle brakes.

Muzzle brakes/compensators are designed to reduce what is called the ' free recoil velocity' of the weapon. The free recoil velocity is how fast the gun comes back at the shooter. The faster a gun comes back, the more painful it is for the firer as the body has less time to absorb the recoil.

Weapons firing fast small-calibre bullets generally have a smaller recoil velocity than larger-calibre slow-moving bullets.

The following examples of recoil energy and velocity are all measured in 8 lb rifles (Table 1.2).

Table 1.2 Recoil energy and velocity for various rifle calibres.




Recoil energy

Recoil velocity

weight (g)

velocity (ft/s)

(ft lbs)


6 mm Rem





270 Win










0.35 Whelen





0.450 Marlin





0.458 Win Mag





There are numerous types of recoil reducer from the simplest, a short length of tube attached at 90 ° to the end of the barrel to divert the gases sideways, to laser-cut slots in the muzzle end of the barrel (Magna Porting).

In conventional designs, combustion gases depart the brake at an angle to the bore and in a slightly rearwards direction. This counteracts the rearward movement of the barrel due to recoil as well as the upward rise of the muzzle. The effect can be compared to reverse thrust systems on aircraft jet engines. The mass and velocity of the gases can be significant enough to move the firearm in the opposite direction of recoil.

On the AKM assault rifle, the brake is angled slightly to the right to counteract the sideways movement of the gun under recoil.

A major disadvantage of recoil reducers is, however, the large increase in noise levels and the gas blast which directs back towards the firer.

One other problem with high-powered rifles such as the Barrett 0.50 Browning is the violent disruption of debris from the ground which can expose the firer's position. This is only a significant factor in military or law enforcement tactical situations.

1.2.10 Flash hiders

When a gun fires, only about 30% of the chemical energy released from the propellant is converted into the useful kinetic energy of actually moving the projectile down the barrel. Much of the remaining energy is primarily contained in the propellant gas-particle mixture which escapes from the muzzle of the gun in the few milliseconds before and after the bullet leaves the barrel.

This extremely hot mixture of incandescent gases and partially burnt propel-lant ignites on contact with the air causing an intense 'muzzle flash'. This can be disconcerting for the firer and a distinct disadvantage under night-time military or law enforcement tactical situations. Not only does it temporarily destroy the firer's night vision, but it also pinpoints his position for the enemy.

Flash hiders either physically hide the flash by way of a cone-shaped device on the end of the barrel (e.g. Lee Enfield No.5 Jungle Carbine) or by dispersing the flash upwards or sideways via a series of fingers or a tube containing longitudinal cuts (M16 rifle).

These attachments are often dual-purpose items designed to suppress the flash of firing and also to reduce recoil.

1.2.11 Muzzle counter weights

These are only used on highly specialized target weapons and are designed to add stability in sighting as well as to reduce the recoil-induced upward motion of the barrel.

1.2.12 Grenade discharger

In its simplest form, this is cup attached to the end of a rifle barrel into which a grenade can be launched via a blank cartridge. Utilizing this device, grenades can be propelled to much greater distances than by throwing alone.

More modern devices can be used with bulleted rounds and contain aluminium or mild steel baffles to capture the bullet.

1.2.13 Recoil booster

Very few of these have been manufactured, the most notable being the muzzle attachment to the German WWII MG 34 machine gun. This attachment was intended to increase the rate of fire in this short recoiling weapon.

Some recoil- operated semi- automatic pistols also have to be fitted with a recoil booster to compensate for the additional weight of the suppressor. Without a booster, short recoil pistols will not function in the self- loading mode of operation.

1.2.14 Brief glossary

Automatic or fully automatic

Blowback action Bolt action Disconnecter

Double action

Drilling Headspace

Locked breech or delayed blowback

Correct terminology for a weapon which continues to fire until the trigger is released.

Simple form of self-loading pistol in which a spring retards the opening of the action after firing.

A method of closing the breech, generally involving a turning bolt.

A mechanism in self-loading weapons which requires the trigger to be released and re-pulled between each shot, thus preventing the weapon from firing automatically. Revolver mechanism where one long pull on the trigger rotates a fresh chamber in front of the firing pin, cocks then drops the hammer, all in one operation. German name for a three-barrelled long arm with a combination of smooth and rifled barrels.

The distance measured from the part of the chamber that stops the forward movement of the cartridge and the face of the bolt.

A weapon in which a mechanical delay is incorporated to ensure that the breech block cannot move back until the pressures in the barrel have subsided to a safe level.

Machine gun


Revolver Rifle

Semi-automatic or self-loading


Single-action Sub-machine gun Vierling

Fully automatic weapon which will keep firing until the pressure is released from the trigger; normally designed to fire rifle calibre ammunition.

In English terminology, all handguns are pistols; some are revolving, some single shot and some self-loading. In American terminology, refers to a self-loading handgun.

Handgun in which the magazine is a revolving cylinder behind the barrel.

Long-barrelled weapon with a rifled barrel. Weapon which uses a portion of the energy of discharge to eject the empty cartridge case, reload a fresh round into the chamber and cock the action ready for firing.

Smooth-bore shoulder firearm designed to fire cartridges containing numerous pellets or a single slug; can be of any calibre from 0.22" upwards.

Revolver mechanism where the hammer has to be manually cocked to rotate the cylinder.

Automatic weapon, firing pistol ammunition, generally 9 mm PB, of a size in between a pistol and a rifle.

German nomenclature for a long arm with two barrels, one of which is for shotgun ammunition and the other for rifle ammunition.

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