# Return pipe

The barrel recoil is a device on guns that makes the barrel movable relative to the mount and thus absorbs the recoil .

In the case of automatic handguns , which function as a recoil loader with a locked bolt, a corresponding mechanism, as an unlocking device, separates the barrel and bolt.

## history

Up until the end of the 19th century, gun barrels were rigidly connected to the carriage in the longitudinal direction. Due to the recoil force that occurred when firing, the cannon usually ran back a few meters, so that it had to be brought back into position and realigned. This significantly reduced the rate of fire and allowed shooting only from gun positions that allowed reverse travel.

Prussian foot artillery around 1885 with wall mount and locking wedges
Krupp mountain cannon 1906, the cradle under the tube placed on elevation

A simple system to compensate for the recoil force and use it to retrieve the gun was recoil wedges. These wedges were used for several decades, even under wartime conditions (1870–71 and 1914–18). The recoil of the shot drove the gun up the wedges and after reaching top dead center it almost returned to the original firing position with the help of the artillerymen. This made it easier to set up the weapon again.

As a first remedy, towards the end of the 19th century, a movable earth spur was attached to the tail of the carriage , which was rammed into the earth, braking the gun by spring force and bringing it back into position. The principle of the spring-loaded earth spur did not prove itself. A rigid ground spur is still used to dissipate forces.

Even first attempts with a barrel (return) brake were unsuccessful, as a very short return path was chosen, which allowed shooting with large barrel elevations, but due to the high braking forces led to the carriage jumping at low barrel elevations.

In 1888, the German engineer Konrad Haußner proposed a hydropneumatic braking and recovery device in a memorandum at Krupp. However, Haußner's principle was rejected, whereupon he left Krupp, patented his invention in 1891 and joined the Magdeburger Grusonwerk AG Buckau , where some prototypes were built until 1893. Similar devices had been developed in France a few years earlier, albeit in an imperfect form. After the takeover of Gruson by Krupp in the same year, however, the project was discontinued.

The first gun suitable for field service with a barrel return was a French 75 mm field cannon, which was introduced into the French army in 1897 as the Canon de 75 mle and used in large numbers during the First World War.

Heinrich Ehrhardt , founder of the Rheinische Metallwaren- und Maschinenfabrik Akt.-Ges. (later Rheinmetall ) hired Konrad Haußner in 1895. After various tests, Rheinmetall developed a variable hydropneumatic braking and retrieval device in 1898 that adapted the return path to the pipe elevation. The resulting improved rate of fire led to the conversion of almost all armies to guns with barrel return (in the German Reich from 1904).

Nowadays, practically all heavy weapons are equipped with a barrel return, barrel brake and barrel retractor . Otherwise the high load on the mount from the shot would not be manageable (for example, the mount of the light field howitzer 105 mm would be loaded with up to 2310 kN with rigid storage). Exceptions are mortars that only fire in the upper corner group. With these, the recoil force is completely transferred to the floor via a base plate.

## functionality

On the gun carriage rests a cradle (upper carriage) which the recoil brake and the retractor, and recuperator receives called. The gun barrel is connected to the upper mount. When firing, the gun barrel slides back and is braked by the barrel brake. This usually consists of a hydraulic cylinder in which the liquid flows through a perforated plate. A second, movable perforated plate controls the size of the passage openings depending on the pipe elevation. Furthermore, the return springs or a pneumatic cylinder (air reclaimer) are pressed together; these bring the pipe back to its original position. The return balance of the barrel is often additionally reduced by a muzzle brake. Residual energy is diverted into the ground by earth spurs .

When using springs, one speaks of a hydromechanical , when using one or more air cylinders, of a hydropneumatic pipe return.

### Balance of power

In a sufficiently precise approximation, the weight forces can be neglected because the inertia forces are considerably greater. This results in the unbraked return pipe:

${\ displaystyle v_ {R} = {\ frac {m_ {G} + 0.5m_ {L}} {m_ {R}}} v_ {0}}$

With

${\ displaystyle m_ {G} = {\ mbox {Ground floor}}}$

${\ displaystyle m_ {R} = {\ mbox {pipe dimensions}}}$

${\ displaystyle m_ {L} = {\ mbox {Mass of charge}}}$

${\ displaystyle v_ {R} = {\ mbox {pipe speed}}}$

${\ displaystyle v_ {0} = {\ mbox {Projectile speed at the mouth}}}$

## Individual evidence

1. Konrad Haußner: The field gun with long barrel return: history of my invention. R. Oldenbourg, Berlin / Munich 1928.
2. Christian Brandau: The importance of Rheinmetall for the German armaments market. 1903-1966. Ruhr University Bochum, 2008. (PDF; 709 kB)