Gas pressure charger
As a gas pressure loader are automatic firearms in which the recharging by means of the combustion of the designated propellant charge of the cartridge resulting gas pressure is raised. Alternative concepts are recoil chargers , in which the recoil energy of the projectile is used as a drive, or weapons with an external drive (e.g. chain gun ) that require an external drive - usually an electric motor .
Although the term gas pressure charger physically stands for different drive variants, sometimes only locked gas pressure chargers or even only gas pressure chargers with bore holes are implicitly meant in the literature. Also, unlocked gas-operated boosters are sometimes incorrectly physically categorized as recoil boosters.
After the ignition of the propellant charge, the pressure of the combustion gases spreads in all directions. On the one hand, the bullet is propelled forward while the case base is pushed backwards. This expanding gas is used to drive the shutter . The mass closure is based on the inertia .
There are basically two types of unlocked gas pressure boosters; on the one hand back pressure loader , on the other hand blow forward ("pre-pressure loader"). In a back pressure charger, the barrel is rigidly connected to the housing; With Blow Forward it is exactly the opposite, the barrel can be moved forward, while the breech or the support plate is rigidly connected to the housing.
Locked gas pressure chargers have a locked locking system; there are versions with or without barrel bore. If the gas pressure is used while the bullet is in the barrel, a bore hole is required. If the gas pressure is only used when the bullet has left the barrel, there is no need for drilling the barrel.
With barrel bore
Gas pressure chargers with a barrel bore take part of the propellant gas through a bore in the barrel after the projectile has passed the bore. The gas is fed into the gas cylinder or pipe that runs parallel to the barrel via the gas block. Part of the gas pressure is lost for the projectile drive. The high pressure gas unlocks and opens the breech, whereby the empty cartridge case is ejected first . When the bolt is subsequently closed by the recoil spring , a new cartridge is fed into the chamber .
The position of the barrel bore must be matched to the locking system and the strength of the ammunition . As a rule, the barrel bore is in the last third of the barrel so that the pressure and temperature of the propellant gas fall to manageable values beforehand. In the case of pistols (e.g. Desert Eagle ) that fire weaker ammunition than rifles, the barrel bore can be located close to the chamber. The cross-section of the barrel bore is significantly smaller than the inside diameter of the barrel ( caliber ). This increases the speed of the gases, which can lead to overheating and erosion wear.
An advantage of gas pressure chargers is that the locking of the lock can be maintained safely and structurally in a simple manner until the gas pressure has dropped to uncritical values during the barrel. The gases only activate the self-loading mechanism after the projectile has passed the gas port , and due to the inertia of the mechanism, the bolt is unlocked with a sufficient delay. The self-loading mechanism is activated by the gas until the bullet has left the barrel ( dwell time ). Another advantage is the possibility of the pressure taken from the barrel bore z. B. to change by a control valve . This allows z. B. the cadence of the weapon changed or the weapon can be adapted to icing and soiling, different types of ammunition (including rifle grenades ), different lengths of barrel and a silencer . Such a gas pressure regulator can also prevent excessive recoil, wear and feed or ejection disturbances due to too much gas being withdrawn ( overgassing ).
Because of these properties, gas pressure guns are preferably set up for firing relatively strong ammunition. Many rifles, some shotguns and a few pistols use this principle.
Disadvantages in comparison to recoil chargers are the weight and space requirements of the gas piston and gas linkage as well as the contamination of the system caused by the discharged gases, especially in the area of the control valve and the gas extraction hole. This can result in uneven shooting behavior.
The transmission of the force of the gases to the bolt carrier can take place in different ways. There are systems with a piston or gas tube and combinations.
The most common system is the gas piston charger; Here the gases act on a gas piston, which transfers the force to the bolt carrier via a gas linkage. The inventors are the Clair brothers from St. Etienne, who in 1889 patented a construction of a gas pressure charger with gas extraction hole and gas piston under the number 49100 in Germany. Other inventors such as Pitcher and Dewhurst (England) and Unge (Sweden) developed similar systems in the following years. Self-loading mechanisms that work on this principle appeared from around 1890 on machine guns such as the Colt Model 1895 , which works on the same principle as the self-loading pistol patented in 1897 by John Moses Browning , the Hotchkiss M1914 by Benjamin Hotchkiss, based on the invention of the Austrian Adolf Odkolek from Újezd , the Lewis Gun from Colonel Isaac Lewis and some other constructions. The gas piston, gas linkage and bolt carrier can consist of several components or, as in the AK-47 assault rifle, for example , be combined into a single component. There are systems with a dedicated return spring for the gas piston, but in many cases this is dispensed with and this task is taken over by the closing spring. The gas pressure device is usually attached above the barrel, because there it is not in the way of the magazine feed. But it can also be attached below the barrel, such. B. machine guns that insert the ammunition belt laterally.
There are systems in which the gas piston is connected to the bolt carrier ( long-stroke piston ) and therefore both travel the same distance, e.g. B. AK-47, and those in which the gas piston moves separately from the bolt carrier and covers a shorter distance (English. Short-stroke piston ), z. B. HK416 . Here a pulse piston with a relatively short stroke transfers the kinetic energy to the bolt carrier, which covers the rest of the distance required for repeating due to its inertia.
A different technical variant has been implemented for some gas pressure guns , in which the gases are led through a gas tube into the interior of the weapon and there act directly on the bolt carrier ( direct impingement ). The first serial weapon with such a pistonless gas system was the Swedish rifle Ag m / 42 , it was later also used in the French MAS-49 rifle and the standard rifle of the US armed forces M16 . The elimination of gas pistons and gas rods enables a noticeable weight saving with this principle, but hot gases and powder residues get directly into the weapon, which harbors the risk of malfunctions due to deposits. For this reason, the M16 rifle in particular only achieved sufficient reliability after extensive development work, but without reaching the functional reliability of gas piston loaders. In addition, the lock and the lock carrier are heated by the returned hot gases. If the shooter wants to use the weapon after shooting e.g. B. dismantle due to a malfunction, he may have to let the weapon cool down in order not to burn himself. The cocking slide can also be too hot to touch, such as B. the AR-10 . With the AR-15 it was therefore placed behind the upper part of the housing. The heat can lead to the tempering of metal parts such as the bolt, bolt carrier and extractor , which reduces the wear resistance and thus the service life. The risk of a cook-off also increases . The gun oil can also evaporate. Furthermore, there is a risk that the weapon will be destroyed if there is water in the gas tube or barrel when the shot is released, which poses a high risk of injury to the shooter. In addition, the hot gas flowing out of the ejection port can be a problem , especially for left-handed shooters. For these and other reasons there are various gas piston conversion kits for the AR-15 alone.
Some weapons combine the systems with gas pistons and gas pipes, in that the gas pipe is led to the breech, but there only acts on a short gas piston, the gas plunger.
Without barrel drilling
Another design works without a barrel bore and instead uses the gas pressure at the barrel muzzle . The drive elements must be at the mouth, z. B. in the form of a gas nozzle. The gases escaping from the mouth are accumulated in the gas nozzle and the resulting movement is directed backwards. Since the gas forces at the muzzle are smaller than in the barrel, the driving forces in this design are lower than in a gas pressure charger with a barrel bore. The transmission path is also longer, because the forces have to be led from the muzzle over the entire length of the barrel to the breech. This means that the delay times are longer and the rate is lower than with a gas pressure charger with a barrel bore. On the other hand, this construction is very safe because the reloading process can only start when the bullet has left the barrel.
There are two variants of the gas pressure charger without a barrel bore; with fixed and movable barrel.
In the variant with a fixed barrel, a movable annular piston surrounds the barrel in front of the muzzle. The annular piston is in turn enveloped by a fixed sleeve that merges into a gas nozzle at the barrel muzzle. When the shot is fired, the gases built up in the gas nozzle push the ring piston backwards and actuate the self-loading mechanism via a push rod. A weapon that works on this principle is the Gewehr 41 . The system was discontinued because of many disadvantages in terms of reliability.
In weapons with a movable barrel, the barrel itself is used as a piston and drive element at the same time. Here, too, a gas nozzle is attached in front of the mouth. When firing, the gases built up in the gas nozzle apply pressure to the muzzle surface. This pushes the movable barrel backwards and releases the lock of the breech. Weapons that only work according to this principle have also not caught on. However, this principle is often used in weapons with combined bolt drives as a recoil amplifier to reinforce the recoil loader . An exception are recoil chargers, which should work with blank cartridges . Since no bullet moves in the barrel, the recoil principle can be used. Then a maneuver cartridge device, which simulates the function of a recoil amplifier, takes care of the reloading function.
Some other designs did not catch on, such as some systems in which the self-loading mechanism was actuated by the gas pressure in the cartridge case. The Swiss Georg Raschein presented such a system in 1894, in which the firing pin and bolt were driven backwards by a movable primer.
In the late 1960s this concept was taken up again in the USA; Irwin R. Barr developed it under the name "Piston Primer" ("piston primer"). The aim was to develop weapons with very high cadence that could not be achieved with conventional gas pressure charging systems. When the shot is fired, a movable ignition bell is pushed out of the case base by the gas pressure. The firing pin is pushed back while the bolt is still closed. After it has covered a certain distance, the firing pin unlocks the bolt.
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