Recoiloperated guns

In recoil-operated systems, which may be of short-recoil or long-recoil types, the energy to drive the reloading cycle comes from the recoil force generated by firing the gun. Part of the gun is designed to recoil against the remainder, compressing a spring, as the breech is opened and the fired case extracted and ejected; the energy stored in the spring is used to drive the bolt back into battery, thrusting a fresh cartridge into the breech as it does so. A key point is that the bolt is mechanically locked to the breech at the instant of firing and remains so until the projectile has left the barrel, thereby ensuring that the breech cannot open until the gas pressure in the barrel has dropped to a safe level.

The difference between long and short recoil is that in the former, the barrel travels all the way back with the bolt before being unlocked. The barrel is then pushed forward by a spring, extracting and ejecting the spent case. The bolt is pushed forward by a second spring once the barrel has returned to battery, collecting and chambering a new cartridge as it does so, and is locked to the breech again before the next shot is fired. In the short-recoil mechanism, the barrel travels only a few millimetres (or centimetres in large cannon) before the bolt is

Vickers Pom Pom

37mm Vickers-Maxim Mk 1 Pom-pom'

(Courtesy: MoD Pattern Room)

37mm Vickers-Maxim Mk 1 Pom-pom'

(Courtesy: MoD Pattern Room)

The Maxim is significant because it was the first automatic machine gun, i.e. not manually powered, and because it saw such widespread use. It was first invented by Hiram Maxim, an American living in England, in 1884. The gun was immediately successful and by 1891 had become the standard machine gun of the British Army. A 37mm cannon version, popularly known as the Tom-pom, because of its distinctive sound on firing, was also produced and saw extensive international service.

The mechanism utilises a toggle joint, which is similar in principle to an elbow joint. The bolt is hinged in the middle so that it can bend like an

RECEIVER

BARREL EXTENSION

OPERATING LINK FIXED TO THE RECEIVER

RECEIVER

BARREL EXTENSION

OPERATING LINK FIXED TO THE RECEIVER

Bolt Rifle Locking Lugs

OPERATING LINK PIVOT POINT

FIRED CARTRIDGE

BOLT

CONNECTING LINK

REAR LINK

BARREL EXTENSION

Action of the Fixed Link on End of Recoiling Bolt Causes It To Unlock

LOCKING LUG

FIRED CARTRIDGE

OPERATING LINK PIVOT POINT

BOLT

CONNECTING LINK

REAR LINK

BARREL EXTENSION

Action of the Fixed Link on End of Recoiling Bolt Causes It To Unlock

Toggle-bolt short-recoil mechanism ( Furrer) (BuOrd, USN)

elbow, but when the gun is ready to fire the bolt is manufactured by Eidgenössische Waffenfabrik of straight, like an outstretched arm. On firing, the Berne.

bolt and barrel recoil backwards together for a few

Early in the twentieth century, the design was millimetres until a part of the mechanism forces the refined by Vickers to create the Vickers-Maxim, joint to bend. At the same time, the rearward move- later known simply as the Vickers machine gun.

ment of the barrel is stopped. As the bolt bends, the This remained the standard medium machine gun head is pulled back away from the breech, extract- of the British Army until 1956. Apart from special ing the fired case. A spring then straightens the bolt, applications, such as air-cooled aircraft variants, it which chambers a fresh cartridge on the way back. It was therefore the first member of the short-recoil family. The Luger pistol uses the same toggle bolt was generally water-cooled, belt-fed and mounted on a sturdy tripod for accurate long-range fire. Although best known in its rifle-calibre version, principle, as did several Swiss cannon of the 1930s it was also made in larger calibres. The 37mm Portland 1940s in 20ntnt, 24mm and 34ntnt calibre. pom was used by all sides in the First World War These were designed by Colonel Adolf Furrer and and Vickers .5" machine guns saw service in the

Vickers Type 40mm

Sectioned MG 131 mechanism showing curved cam-track for unlocking the holt (Courtesy: MoD Pattern Room)

Pom Pom 37mm
The 'Pom-pom ' family of cartridges (from left to right): 37mm Maxim (37 x 94 R), 3.7 cm So eke I flak (37 x 101SR), lpdr Vickers Mk 111 (37 x 69R), VSN Heavy One-Pounder (37 x 137 R), l'Apdr Vickers (37X123R), 2pdr Vickers (40 x 158R)

Second World War, but these were eclipsed in importance by the naval 2pdr (two-pounder, after the projectile weight) gun of 40mm calibre, which inherited the Pom-pom nickname. Other nations also adopted the Maxim or the Vickers and there are undoubtedly many Maxim-type machine guns still giving good service all around the world today, even though their heyday was over by the end of the Second World War.

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