The barrel is the main part of small arms. The barrel of a rifled small arms is designed to impart a rotational and translational movement to the bullet at a certain initial speed in a certain direction due to the energy of the powder charge. The rotational movement of the bullet, which provides it with gyroscopic stability in flight, is given so that it flies steadily with the head part forward and does not overturn under the action of the force of air resistance. The combination of barrel and cartridge determines the ballistic qualities of the weapon.
The device of the barrel is determined by the purpose of the weapon and the peculiarities of its operation. The barrel as part of the weapon works under special conditions. In order to withstand high pressure of powder gases at high temperatures, friction of the bullet during its movement in the bore and various service loads, the barrel must have sufficient strength, which is provided by the thickness of its walls and material and the ability to withstand high pressure of powder gases 250 - 400 MPa (up to 4000 kg / cm 2) at temperatures up to 3000 ° C. During the combat use of the weapon, the barrel is subjected to various loads (with a bayonet strike, since the bayonet is attached, as a rule, directly to the barrel; during the combat use of weapons, including when firing from an under-barrel grenade launcher; when it falls, etc.). The outer outline of the barrel and the thickness of its walls are determined by the conditions of strength, cooling, the method of fastening the barrel to the receiver, mounting on the barrel of sighting devices, flame arresters, muzzle brakes, as well as parts that protect against burns, handles, barrel linings, etc.
On the barrel, breech, middle and muzzle parts are distinguished. The muzzle (front) part of the barrel ends with a muzzle cut. The muzzle of the barrel is a cross-section passing through the front end of the barrel without taking into account the flame arrester (compensator, muzzle brake). The shape of the muzzle eliminates accidental damage to the rifling, impairing the accuracy of shooting. The back of the barrel is called the breech, and the rear end of it is the hemp of the barrel.
Inside the barrel has a through channel, which contains: a chamber, which serves to accommodate the cartridge; a bullet inlet, which is a transitional section of the barrel bore from the chamber to the rifled part; and the threaded part. The bores of the barrels of various types of weapons are approximately the same in design and differ only in the shape of the chamber, the caliber and the number of rifling. The chamber corresponds to the shape and dimensions of the case, and its design is determined by the way the case is fixed in it. The chamber must ensure free entry of the cartridge, good fixation of the sleeve and obturation of the powder gases, as well as sufficiently free extraction of the sleeve after the shot. On the other hand, the gap between the case and the chamber walls should be kept to a minimum, as too much clearance can cause the case to rupture.
To ensure tight fixation of the sleeve, the longitudinal dimensions of the chamber are appropriately selected, and the values of these dimensions are determined by the method of fixing the sleeve (along the edge, along the front slope), which, in turn, depends on the design of the latter.
A section of a Walter P.38 pistol in the chamber of the barrel of which the cartridge is fixed by the front cut of the sleeve
If the sleeve has a protruding edge (flange), then usually fixation is carried out by resting this edge on the trunk stump. With this method of fixing, large errors are allowed in the longitudinal dimensions of the chamber and the cartridge case itself. However, such casings usually complicate the mechanisms for feeding cartridges and are currently rarely used, although it is for the domestic 7.62-mm rifle cartridge, which has a sleeve with a protruding rim, that all easel and single machine guns are designed: SGM, PK / PKM, PKB, PKT, as well as an SVD sniper rifle.
If the sleeve has a non-protruding edge (flangeless), then usually fixation is carried out by sliding the sleeve into the slope of the chamber. In this case, there is a need for a sufficiently accurate manufacture of the chamber slope, which makes it necessary to increase the accuracy of the manufacture of the chambers and casings. Examples of this are the flangeless 7.62 mm submachine gun mod. 1943 and 5, 45-mm cartridge 7N6 used in Kalashnikov assault rifles and light machine guns.
For pistol cartridges, the sleeve fixation is most often carried out by the front cut of the sleeve neck. This fixation provides the most simple chambering device in the presence of a sleeve without a protruding rim, but is unreliable for other types of cartridges. Therefore, it only applies to pistol cartridges with cylindrical sleeves, for example, a 9mm pistol cartridge for a PM pistol.
In most types of automatic weapons, the beginning of the extraction (extraction) of the sleeve occurs at a time when the pressure of the powder gases in the barrel is still quite high. Good obturation of powder gases is carried out by tight fit of the walls of the case to the walls of the chamber for a sufficiently long length. For this purpose, in cases where the sleeve moves back at a high pressure of the powder gases (in systems with a free and semi-free breech block), sometimes a cylindrical surface is made in the rear of the chamber, which eliminates the breakthrough of the powder gases even with large displacements back. Such a surface significantly reduces the jamming of the tapered part of the sleeve in the chamber after the shot and after the decay of the longitudinal deformations of the locking unit, since the sections of the bottom of the sleeve are usually exposed to the greatest jamming. In some types of weapons, the frictional forces between the cartridge case and the chamber can be so great that when the cartridge is removed, lateral rupture or damage to the rim by the ejector can occur. To reduce the indicated friction forces, sometimes Revelli grooves are used in the chambers, which, by creating back pressure on a certain part of the outer surface of the sleeve, facilitate its extraction (extraction). Due to the complexity of manufacture, rapid contamination and difficulty in cleaning, Revelli grooves are rarely used in modern weapons.
The bullet inlet connects the chamber with the rifled part of the barrel and serves to accommodate the head of the bullet in order to ensure its smooth penetration into the rifling of the barrel. In a rifled weapon, the bullet entrance consists of two cones, the first of which reduces the diameter of the chamber to the diameter of the rifling fields. The second cone serves to ensure the gradual penetration of the bullet into the rifling (this cone is absent in smooth-bore weapons). The accuracy of the weapon battle largely depends on the size and shape of the bullet entrance. The length of the bullet entrance ranges from 1 to 3 gauges.
Caliber is a unit of measure used in a weapon to measure the inside diameter of the barrel bore and the outside diameter of a bullet. The caliber of a rifled barrel is defined as the distance either between two opposite edges of the barrel, or between two opposite grooves. In Russia, the caliber of a barrel is measured by the distance between two fields. In this case, the caliber of the bullets in relation to the weapon exceeds the caliber of the barrel in order to ensure that the bullet cuts into the rifling for the bullet to acquire a rotational motion. So, the diameter of the barrel of the Makarov PM pistol in the rifling fields is 9 mm, and the diameter of the bullet is 9, 2 mm. The caliber of the barrel of a weapon is indicated in the system of measures adopted in the country of manufacture of the weapon. Countries with metric units use millimeters, and countries with imperial units use fractions of an inch. So, in the USA, the caliber is indicated in hundredths, and in the UK - in thousandths. In this case, the caliber is written as an integer with a dot in front, for example, the American Colt M 1911 A1 pistol in.45 caliber.
Different types of rifling are adopted in different armies. In the Soviet Union / Russia, the rifling shape is rectangular in cross-section, with the rifling depth being 1.5-2% of the weapon caliber. The rest of the rifling profiles are used in various foreign samples, for example, the trapezoidal profile - the Austrian 8-mm magazine rifle Mannlicher M 95; segment profile - in Japanese 6, 5-mm magazine rifles Arisaka type 38; oval profile - by Lancaster; beveled profile - in French 7, 5-mm machine guns Chatellerault M 1924.
The direction of the rifling in the barrel can be right (in domestic samples) and left (in England, France). The different direction of the grooves has no advantages. Depending on the direction of the rifling, only the direction of derivation (lateral deflection) of the rotating bullet changes. In domestic small arms, the right direction of the rifling is adopted - from left to top to right as you move along the bore from the breech to the muzzle. The angle of inclination given by the grooves provides a rotational movement of the bullet, while its stability in flight depends on the speed of rotation of the bullet. The length of the rifling stroke (the length of the bore at which the rifling makes a full revolution) also has a significant effect on the accuracy of fire. The rifling pitch of the AKM assault rifle is 240 mm, the DShKM machine gun is 381 mm, and the KPV machine gun is 420 mm.
The length of the rifled part of the barrel of each weapon sample is selected from the condition of obtaining the required initial bullet velocity. The use of the same cartridge in samples of weapons with different barrel lengths allows you to obtain different initial bullet velocity (See table).
It can be seen from the table that the range of a direct shot increases with an increase in the initial speed for the same cartridge, which affects the improvement of the flatness of the trajectory and an increase in the affected area. With an increase in the initial velocity, the effectiveness of the bullet on the target increases due to the greater energy of the bullet. So, at a distance of 1000 m, a bullet emitted from the barrel of a PK machine gun has an energy of 43 kgf / m, and a bullet ejected from the barrel of a machine gun has an energy of 46 kgf / m.
In a shotgun hunting weapon, the bore guide is smooth (without grooves), and its muzzle can be narrowed (conically or parabolic) or widened. The narrowing of the canal is called a choke. Depending on the size of the constriction, which improves the accuracy of fire, distinguish between payday, medium choke, choke, strong choke. An expansion in the muzzle, called a bell, increases the dispersion of the shot and can be tapered or otherwise shaped.
Barrels in small arms are structurally different into barrels - monoblocks and fastened barrels. Barrels made from a single piece of metal are called monoblock barrels. However, to increase the strength of the barrel, they are made from two or more pipes, put one on top of the other with an interference fit. Such a trunk is called stapled. The fastening of barrels is not widely used in automatic weapons due to the complexity of manufacture. The interference fit of the barrel to the receiver can be considered as partial fastening.
Rational barrel cooling for modern automatic weapons is extremely important. The leading parts of the bullet, cutting into the grooves, receive significant plastic deformations and thus exert additional pressure on the walls of the barrel bore. The wear of the barrel bore is caused by friction against its surface of the shell of a bullet moving with a high frictional force at a high speed. Moving after the bullet, and also partially breaking through the gaps between the walls of the barrel and the bullet, the gases produce an intense thermal, chemical and erosive effect on the barrel bore, causing its wear. The rapid abrasion of the surface of the barrel bore leads to the loss of some properties necessary to ensure the effectiveness of firing (the dispersion of bullets and projectiles increases, stability is lost in flight, the initial velocity drops below a predetermined limit).
With strong heating of the barrel, its mechanical qualities decrease; the resistance of the barrel walls to the action of the shot decreases; this leads to increased metal wear and a decrease in barrel survivability. With a very hot barrel due to the appearance of ascending air currents, aiming is difficult. High breech temperatures can cause a cartridge that is sent into the chamber after stopping firing to heat up to spontaneous combustion, making it unsafe to handle the weapon. In addition, the high heating of the barrel makes it difficult to operate the weapon. In order for the shooters not to suffer from burns, special shields, handles, etc. are mounted on the weapon.
The high temperature of the powder gases is due to the rapid heating of the barrels of automatic weapons during firing. It follows that the intensity of heating the barrel depends on the power of each shot and the mode of fire. For weapons designed for single shooting with low-power cartridges (pistols), barrel cooling is of secondary importance. For weapons firing powerful cartridges (machine guns), the cooling should be the more efficient, the larger the magazine (tape) capacity and the longer continuous firing should be from a given weapon. An increase in the barrel temperature above a certain limit reduces its strength characteristics and service life. All this ultimately limits the mode of fire (that is, the permissible number of shots during continuous shooting).
Special methods of barrel cooling include: quick replacement of a heated barrel with a cooled barrel; increase in the cooling surface of the barrel due to the ribs; the use of various types of nozzles (radiators) for the same purpose; artificial blowing of the outer or inner surface of the barrel; the use of liquid coolers, etc. At present, two types of barrel cooling are most widely used - air and water.
Sectional view of the Colt M 1911A1 pistol, where the barrel detaching during disassembly is attached to the frame with an earring
Air cooling has become the most widespread among modern weapons due to its simplicity, but it does not provide a high rate of heat transfer to the air.
To increase the heat transfer of the barrel, its surface is usually increased using special transverse or longitudinal ribs. The effectiveness of this method is determined by the size and number of the barrel ribs. Although the use of fins on the outer surface of the barrel increases the total area of heat exchange with air, it leads to uneven heating of the barrel metal and ultimately reduces its total heat capacity. However, the increase in the ribs of the trunk leads to its heavier, which is disadvantageous. Attempts are known to use ribs made of light alloys worn on the barrel. However, this method has not become widespread due to the complexity of the manufacture of such barrels. To increase heat transfer, devices were designed that improved air circulation by blowing the barrel bore and blowing its outer surface. For example, in the English light machine gun Lewis M 1914, a radiator with longitudinal ribs made of light alloy was put on the barrel, and a casing in the form of a pipe was put on the radiator. During firing, a jet of powder gases coming out of the barrel formed a vacuum in the front of the casing, as a result of which air was sucked into the casing from behind and passed between the ribs, increasing the intensity of their cooling. The use of such a design increased the cooling intensity of the barrel during firing, however, it was found that in the intervals between bursts, the casing prevented the flow of fresh air, which ultimately did not lead to an improvement in barrel cooling.
Currently, modern models of automatic weapons with air-cooled barrels (large-caliber machine guns) often do not have ribs on the barrel or they are made very small, using rather massive barrels, for example, in the Austrian 5, 56-mm assault rifle AUG, a screw thread is simply rolled on the barrel in increments of approximately 1 mm. For light weapons (assault rifles and light machine guns), either the fire mode is limited, or (for light and heavy machine guns), quick-change barrels are used, which allow you to quickly replace the heated barrel in a combat situation and thereby ensure a high firing mode. In this case, the barrels of automatic weapons have, as a rule, large reserves of strength. A thicker barrel, having a higher heat capacity, heats up less from shot to shot, which increases the duration of continuous fire until a dangerous overheating of the barrel is reached and increases its service life. In this regard, the barrels for the same cartridge in weapons intended for use in a hard mode of fire (for example, single PK / PKM machine guns) have a thicker barrel than in weapons that have a relatively low practical rate of fire (SVD rifle).
Especially effective is the water cooling of the barrels, which in the past was widely used in heavy machine guns. Its feature is a sharp decrease in the temperature of the barrel with minor interruptions in shooting due to the intense transfer of heat from the barrel to the coolant. To cool the barrel of a normal caliber machine gun, it is enough to have a supply of water in the casing of the order of 3-4 liters, and for a large-caliber machine gun 5-8 liters. Such a cooling system allows for continuous fire until all the water has boiled away. However, the presence of a casing with water greatly complicates the design of the weapon and its operation, and also increases the vulnerability of the weapon itself in battle. An example is the domestic 7, 62-mm machine gun Maxim arr. 1910 In addition, water cooling of the shaft has a number of disadvantages: a constant supply of water is required; at low temperatures, water freezes, which can damage the casing and barrel; the mass of weapons increases at the expense of maneuverability; the complexity of preparing weapons for firing; high vulnerability of weapons in battle, etc.
Due to these shortcomings, water cooling of barrels is not used in modern small arms, but it is successfully used in automatic weapons of a stationary type, for example, in ship installations.
There are two main types of attachment of the barrel to the receiver: a detachable connection of the barrels with the receiver of the weapon, which provides for a quick change of the barrel without disassembling the weapon, and one-piece, which does not.
In most modern models of small arms, the service life of which is the same as that of the barrel (SVD rifles, AKM / AK-74 assault rifles, RPD / RPK / RPK-74 light machine guns and PM pistols), which do not have a device for a quick barrel change, the barrel is connected to the receiver by a one-piece connection. This can be a threaded connection with an interference fit, as, for example, in a self-loading Dragunov rifle, or mating a cylindrical surface with an additional pin. In this case, the assembly of the barrels with the receiver is carried out at the factory.
The barrels that are detached during disassembly can be fastened using a bayonet and threaded connection, an earring or a hairpin. The latter two are used in some guns for ease of disassembly and cleaning. An example is the fastening of the barrel of a Tokarev TT pistol. In addition, detachable connections between barrels and receivers (which do not provide quick barrels change) are usually used in easel, single and large-caliber machine guns PK, KPV, DShKM, NSV and their modifications. Detachable connections allow, during the operation of the weapon, to replace heated barrels with spare ones and thereby make it possible to conduct intensive and prolonged fire (while shooting is being made from one barrel, the other is cooled). In addition, the presence of a removable barrel increases the survivability of the weapon.
Spare barrel with a single MG.42 machine gun case
Detachable connections of quick-change barrels with the receiver are usually made with rusk or wedge. These connections are mainly used for light and heavy machine guns. Sugar-threaded connections are most often made with screws, for example, in a 12, 7-mm DShK machine gun mod. 1938 Sometimes when connected, the barrel turns, and sometimes a special coupling. In some cases, the barrel is simply nested with its rusks in the corresponding grooves of the receiver. In systems with a movable barrel, special protrusions on the barrel are sometimes used to attach the barrels to the receiver (spikes in the Maxim machine gun arr. 1910). In addition, the replaceable barrel is also connected to the receiver by a wedge connection. So, in the DShKM machine gun, the barrel is connected to the receiver with a wedge. Despite the simplicity of the design, such a connection is inconvenient in operation, since to replace the barrel it is necessary to unscrew the nut and knock out the wedge. A more advanced design of this type is used in the NSV heavy machine gun. In systems with a fixed barrel - PK / PKM, SGM machine guns and their modifications - an adjustable wedge is used to compensate for the wear of the bolt lugs. By adjusting the distance between the bottom of the bolt cup and the breech cut of the barrel (mirror gap), the bolt completely closes and the appearance of a delay in the form of a transverse rupture of the sleeve when fired is eliminated. In order to facilitate the separation of the barrel from the receiver in a heated state, the outer surface of the breech of the barrels of PKM / PKT machine guns is chrome plated.
Devices for various purposes can be mounted on the muzzle of the barrel. So, on the barrel of AKM assault rifles from 1959 to 1962, a clutch is installed to protect the thread from damage, and a compensator is attached to the barrel of AKM assault rifles from 1963 to 1975 to increase the accuracy of the battle when firing bursts on the move, standing and kneeling. The compensator has a threaded part, which serves to connect with the muzzle of the barrel. The front part of the compensator is made in the form of a projection with an oblique cut. A groove is made inside the protrusion, which forms a compensation chamber. Powder gases after leaving the bore create excess pressure, which deflects the muzzle of the barrel towards the protrusion (downward to the left). The AK-74 assault rifle uses a two-chamber muzzle brake-compensator, which simultaneously serves as a flame arrester, which significantly increased the stability of the weapon when firing. On the barrels of RPK, PK / PKM machine guns, SVD sniper rifle and AKM assault rifle, which are mounted under a night sight, slotted flame arresters are attached, designed to reduce the glow intensity of powder gases heated to a high temperature and burning powder particles when exiting the barrel bore. Reducing the visibility of the muzzle flame is achieved by the fact that most of it is covered by the side walls of the flame arrester. Machine guns PKT, SGM, KPVT, NSV have flame arresters with a conical bell. In this flame arrester, due to the influx of ambient air into it, intensive afterburning of powder particles is ensured and thereby the brightness of the muzzle flame decreases when firing.
The flame arrester of the KPVT machine gun has a more complex design, consisting of the actual flame arrester, the base of the muzzle, the bushing and the piston of the barrel. In this regard, the flame arrester of the KPVT machine gun, in addition to reducing the brightness of the muzzle flame, provides an increase in the recoil energy of the movable barrel.
The muzzle brakes can also be installed on the barrels, designed to reduce the recoil energy of the barrel by diverting part of the powder gases in the lateral directions and reducing its outflow in the axial direction.
On the barrels of weapons, operating on the principle of using the energy of a part of the powder gases discharged through a side hole in the wall of the barrel, gas venting devices are attached. These devices have a narrow inlet part connected with the bore and a widened outlet part - a gas chamber. Gas regulators are installed in the gas chambers of the PK / PKT, SGM, RPD, SVD shafts, ensuring the reliability of the automation in various operating conditions. This is achieved by changing the amount of powder gases acting on the piston of the bolt carrier.
There are the following methods of regulating the intensity of the action of gases on the piston of the bolt carrier:
- change in the area of the minimum cross-section of the gas pipeline through which the gases flow from the barrel into the gas chamber of machine guns (PKT, SGMT). This design of the gas regulator allows you to reduce the gas content inside the tank's combat vehicle;
- discharge of gases from the chamber into the atmosphere (SVD rifle, PK / PKM machine gun). The maximum speed of the bolt carrier will be with the holes closed, since in this case the maximum amount of gases will be supplied to the piston of the bolt carrier.
