Other shortrecoil

MECHANISMS

There are many different ways of locking the bolt to the barrel extension. The strongest is probably the rotating bolt, held by locking lugs on the bolt which fit into recesses in the barrel extension, just as in a bolt-action rifle. During the initial rearward movement of the barrel/bolt assembly, the bolt (or more commonly just the head of the bolt) is forced to rotate by cams until it is unlocked. This system was used by the Rheinmetall-Borsig 3.7cm FlaK 18, 36 and 37, the Mauser MG 151 and the Soviet 14.5mm KPV (Krupnokalibernyi Pulemet Vladimirova; heavy-calibre machine gun designed by Vladimirov) NS-23, NS-37 and NS-45 (designed by Nudelman and Suranov). During the 1960s, a range of rotary-locked short-recoil cannon was developed by Hispano-Suiza. These consisted of the HS 827-B (20 x 139), the HS 827-C (23 X 133), the HS 836 (30 X 136) and the HS 837 (30 X 170), but none was adopted.

Another rotating mechanism is the Solothurn lock (invented by Louis Stange early in the twentieth century), which consists of a rotating collar fitting around the barrel extension and locking this to the bolt by means of an interrupted thread. As the barrel/bolt assembly moves rearwards, the collar is rotated by cams in the receiver, thereby disengaging the lock and enabling the bolt to be separated. The Solothurn lock was used in various infantry weapons developed between the wars and in the SI2-100 2cm cannon. Rheinmetall reclaimed the design in the 1930s and produced an improved version, the MG 204 (initially known as the Lb 204) aircraft gun. This fired the 20 X 105B short Solothurn cartridge which resembled a slightly shortened, belted Hispano (later replaced by a version firing modified beltless 20 X 105 ammunition). The Solothurn lock was also used in the 13mm MG 131, the 2cm Solothurn S18-100 and S18-1000 antitank rifles and the 2cm SI8-350 and 3cm MK 101 aircraft guns.

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

The firm Waffenfabrik Solothurn was established in Switzerland in 1929 as a subsidiary of the German firm Rheinische Metallwaaren-und-Maschinenfabrik, better known by its trade name Rheinmetall, as a way of evading the limitations on weapon development imposed by the Treaty

7cm Tak RheinmetallSolothurn S18 1000 Anti Tank Rifle155 Cannon

The breech bolt moves forward and chambers a fresh round

Browning M1919a4 Recoil Actions

Run out Buffer

Barrel Recoil Free Recoil

Unlocking Cam

Accelerater

Cartridge 20x139

Back Plate Buffer

The round is fired and the barrel and breech block are pushed to the rear by the recoil forces. After a short distance they are unlocked and the barrel is halted. Additional momentum is given to the breech block by an accelerator lever before the barrel stops moving

The breech block moves to the rear of the body of the weapon under its own momentum

The spent case is extracted and ejected, the breech block is halted by the buffer and the barrel is held to the rear

The breech bolt moves forward and chambers a fresh round

Barrel Return Spring

Run out Buffer

Barrel Recoil Free Recoil

Unlocking Cam

Accelerater

Back Plate Buffer

Lever

The barrel and breech block move into the forward position and a round is fed into the chamber

Short-recoil mechanism (Courtesy: D.F. AI bop)

Recoil-operated rotary locking sleeve mechanism

BARREL

COUPLING SLEEVE

BARREL

RETAINING RING

RECEIVER

BARREL

COUPLING SLEEVE

BARREL

RETAINING RING

CAM TRACK SLEEVE IS FIXED TO BARREL COUPLING SLEEVE

22lr Bolt Face

RECEIVER

BOLT PARTLY UNLOCKED

BOLT FULLY LOCKED

CAM FOLLOWER ON LOCKING SLEEVE

BARREL

RETAINING RING

SLEEVE ROTATING CAM TRACK

CAM TRACK SLEEVE IS FIXED TO BARREL COUPLING SLEEVE

BOLT PARTLY UNLOCKED

BOLT FULLY LOCKED

CAM FOLLOWER ON LOCKING SLEEVE

BARREL

RETAINING RING

SLEEVE ROTATING CAM TRACK

BOLT UNLOCKED

BOLT UNLOCKED

Sako Pieces
LOCKING SLEEVE IN UNLOCKED POSITION

BOLT LOCKING LUGS ON SLEEVE

BOLT LOCKING LUGS ON SLEEVE

FIRED CARTRIDGE

Rear Locking Lugs

BARREL HELD TO THE REAR

BARREL

LOCKING SLEEVE IN UNLOCKED POSITION

Cam Groove in Receiver Causes Locking Sleeve To Rotate, Unlocking the Bolt.

FIRED CARTRIDGE

BARREL HELD TO THE REAR

BARREL

LOCKING SLEEVE IN UNLOCKED POSITION

Cam Groove in Receiver Causes Locking Sleeve To Rotate, Unlocking the Bolt.

of Versailles. These nominally Swiss weapons incorporating lugs which fit into recesses in the bolt therefore featured significantly in German rearma- to hold them together. The initial movement of the ment plans. Two years after the acquisition of barrel pivots the lever, lifting the lugs and releasing

August Borsig GmbH in 1933 the firm became the bolt. An early example of this was invented by

Rheinmetall-Borsig, a designation which lasted Louis Schmeisser in the early 1900s and used in the until 1956, after which it re-formed as Rheinmetall. Dreyse machine gun and, in enlarged form, the

An alternative system uses a pivoting lever 20mm Erhardt cannon under development in 1918.

or plate, fixed to the barrel extension and Erhardt was one of the key figures in Rheinmetall,

Aircraft Cannon

2cm Erhardt FlzK aircraft cannon

(Courtesy: MoD Pattern Room)

so this mechanism was incorporated in various Rheinmetall weapons thereafter. Strenuous efforts at the end of the war to keep the Erhardt secret from the Allies were largely successful and few examples survived.

The Erhardt was too late to see service in World War One (although at least fifty-one were made) but the design was eventually passed by Rheinmetall to their Swiss subsidiary, Solothurn, who developed it into the S5-100, in which the design was enlarged to take the long Solothurn 20 X 138B cartridge. This was further developed into the important FlaK 30, KwK 30 and MG C/30L family. The design was subsequently modified by Mauser to improve the rate of fire, leading to the FlaK 38 and KwK 38.

Another variation is the rising block lock, with that invented by the prolific American John M.

Browning being the most successful. In this case the barrel and bolt are connected by a locking piece which is vertically cammed out of engagement. The Browning short-recoil machine gun emerged during the First World War in rifle calibre as the M1917, later refined into the M1919, in which form it remained in service until well after the Second World War. The same basic design was scaled-up to a new .50" (12.7 X 99) calibre towards the end of the First World War, eventually emerging as the Ml921. Subsequently refined to the M2, this was extensively used by all three services in various versions during the Second World War and has remained in service ever since. The M3 was a postwar aircraft version with a very high rate of fire, achieved in part with the aid of a recoil booster attached to the muzzle.

During the Second World War, the Japanese were great enthusiasts of the American Browning-type aircraft guns and fielded a variety of weapons using this design. The smallest was the army's Ho-103 aircraft gun, scaled down to use the export version of Vickers* .5" cartridge, which for some obscure reason was slightly different from the British service round, being semi-rimmed (12.7 X 81SR). The cartridge was apparently obtained via Italy, which had acquired manufacturing rights for use in the Breda-SAFAT aircraft machine gun. The compact round enabled the gun to weigh only 22kg while firing at 900 rpm from its disintegrating-link belt. This was an impressive combination of small size and power which would have been most useful to the RAF (particularly for bomber defence) if they had thought of developing such a Vickers/Browning hybrid.

Short-recoil guns designed for water-cooling frequently had the barrel supported at the muzzle end via a sliding fit at the front end of the cooling jacket. In air-cooled versions of such guns, a perforated barrel casing often performed the same function, particularly in Browning-pattern weapons.

The later Japanese Navy Type 3 aircraft gun was a direct copy of the .50" Browning except that the calibre was amended to the 13.2 X 99 Hotchkiss already in service as an AA weapon, an easy task as the cartridges were almost identical. Probably the most successful of the Browning copies was the armys Ho-5, scaled up to take a 20 X 94 cartridge,

Sectioned Browning .50" M2 showing chamber

(Courtesy: MoD Pattern Room)

Sectioned Browning .50" M2 showing rear of net ion (Courtesy: MoD Pattern Room)

Browning Copy Plan Pattern

Sectioned Browning .50" M2 showing chamber

(Courtesy: MoD Pattern Room)

Sectioned Browning .50" M2 showing rear of net ion (Courtesy: MoD Pattern Room)

and this was followed into service by the Ho-155 in 30 X 114 and the massive Ho-204 in 37 X 144. All of these were aircraft guns, but the last two saw little use.

Short-recoil mechanisms do not generate much energy for the reloading cycle, which can result in a low rate of tire. It is therefore common for them to incorporate a bolt accelerator, a pivoting lever which kicks the bolt rearwards as soon as it is unlocked. A further problem in belt-led guns is the need for the recoil to lift the ammunition belt from its container and pull it through the gun. As the available power is rather marginal to achieve this, recoil-operated guns (particularly in rifle-calibre versions) are sometimes seen with a bulbous device on the muzzle which uses the power of the escaping propellant gas to boost the recoil - the exact opposite of a muzzle brake. It is popularly known as a muzzle booster, more formally as a recoil intensifies Strictly speaking, this turns it into a gas-assisted recoil-operated gun.

Recoil was the force driving a famous twin-bar-rel gun. As already noted, the first twin-barrel machine guns were manually powered: the nineteenth century Gardners. During the First World gas to operate the mechanism and are therefore War, the German firm Gast devised a different form properly hybrid guns. The GE 225, which has not so of mechanism for an aircraft RCMG, in which the far been adopted for service, was also offered in an recoil of each barrel operated the loading and firing externally powered version.

Mg131 Manual

Muzzle booster on M G 131 (sectioned)

(Courtesy: MoD Pattern Room)

Muzzle booster on M G 131 (sectioned)

(Courtesy: MoD Pattern Room)

mechanism of the other, leading to a high rate of

New short-recoil designs are now very uncom-

fire of around 1,600 rpm. This principle was adopt- mon, having been largely replaced by gas-operated ed in revised form much later, in the Russian GSh- or externally powered designs. One surprising

23 (Gryazev-Shipunov after the designers) and GSh-30 aircraft guns and the 2A38 AA gun, all of exception is the current Russian aircraft cannon which arms the MiG-29 and Su-27 families, the which display the usual national characteristics of GSh-301. Despite many Western sources assuming compactness, light weight and a high rate of fire, that this is a revolver cannon, it does in fact utilise and the American 25mm GE 225. These all use gun a short-recoil mechanism with a sliding-wedge breech. Performance is comparable with Western revolver cannon, while weight is reduced by half and the action is much slimmer.

PROJECTILE

LEAVING

MUZZLE

BOOSTER HOUSING

BARREL (RECOILS)

PROJECTILE

LEAVING

MUZZLE

BOOSTER HOUSING

BARREL (RECOILS)

20x139 Projectile

TRAPPED GASES EXERT PRESSURE ON MUZZLE FACE OF BARREL

BARREL

JACKET (FIXED)

TRAPPED GASES EXERT PRESSURE ON MUZZLE FACE OF BARREL

BARREL

JACKET (FIXED)

Example of a Muzzle Booster.

Operation of a muzzle booster (BuOrd, USN)

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