Rapid Fi Uk

the belt, and the links are designed to fall free of each cartridge as it is chambered. Initially devised in Germany, this was quickly introduced into British service in 1916 (the Air Service Mk I) and was rapidly adopted elsewhere. Not all steel belts have been of the disintegrating type, and some (e.g. for the German MG 131 and 151) were designed to be convertible between disintegrating and non-disintegrating depending on the installation requirements. Disintegrating-link belts can be extended by clipping on additional sections, whereas non-disintegrating ones generally cannot.

Belt design has to take into account a number of factors. The clips must be strong enough to maintain their grip on the cartridges while not being so tight that cartridge extraction is hindered (not always achieved, particularly with aircraft belts subjected to high G forces in violent manoeuvring). The belt must obviously be flexible in the vertical plane but also needs to permit curvature in the horizontal plane to allow for the needs of different installations and for some gun movement relative to the ammunition container. This was of particular importance in aircraft turret mountings, in which ammunition was commonly contained within the fuselage, so the belt feed had to allow for

FEED SPROCKET

SPROCKET

ROTATING

NOTCHES

ANTI-REVERSE LATCH

PIVOT POINT

BARREL

FEED SPROCKET

SPROCKET

ROTATING

NOTCHES

ANTI-REVERSE LATCH

PIVOT POINT

Feed Sprocket

BARREL

OPERATING ROD

VIEW THRU FEED SPROCKET

Lug on Operating Rod Actuates Sprocket Rotating Cam.

OPERATING ROD

SPROCKET ROTATING CAM

VIEW THRU FEED SPROCKET

Lug on Operating Rod Actuates Sprocket Rotating Cam.

Belt feed mechanism for DShK-38 ( BuOrd, USN)

20mm Belt Feed Mechanism

Cloth belt feed for .50" Browning

¡Courtesy: MoD Pattern Room)

Cloth belt feed for .50" Browning

¡Courtesy: MoD Pattern Room)

Apache Feed Sprocket

Steel non-disintegrating belt for DShK-38

fCourtesy: MoD Pattern Room)

Belt feed sprockets in Oerlikon KCB cannon

(Courtesy: MoD Pattern Room)

Steel non-disintegrating belt for DShK-38

fCourtesy: MoD Pattern Room)

both gun elevation and turret traverse. It is common for belt-feed systems to incorporate belt guides to ensure that the belts are fed smoothly into the gun.

The power to move the belt through the gun can be provided in several ways. In HMGs it is usually provided by the movement of the bolt, which drives a mechanism to pull the cartridges into place; some cannon also utilise this method. Alternatively, in cannon fitted to recoiling mountings the recoil movement is often used. A rare variation, demonstrated by the Rheinmetall-Borsig MK 103, involved the drive being taken from the recoiling barrel. Gas can be tapped from the barrel to drive the belt (as distinct from the gun mechanism), or a separate electric or hydraulic motor can do the work. An interesting hybrid was the Chatellerault-based drive for the 20mm Hispano; this was driven by a pre-wound spring, the tension of which was maintained by the gun recoil movement. The advantage of this complexity was a smooth belt-pull, unaffected by the jerkiness of the gun motion. One unusual method, tried (apparently

Belt feed sprockets in Oerlikon KCB cannon

(Courtesy: MoD Pattern Room)

Ammunition belt link types

Dshk Ammunition Belt Links

PUSH THRU LINK

Ammunition Belt Link

PUSH THRU LINK

PUSH DOWN LINK

PULLOUT LINK

PUSH DOWN LINK

PULLOUT LINK

PUSH DOWN LINK

Cal Sniper Rifle
PUSH DOWN LINK

PUSH DOWN LINK

unsuccessfully) in the Ikaria MG-FF, utilised the force of the gas escaping from the muzzle.

The advantage of belt feeding is that large quantities of ammunition can be held ready to fire, limited only by the space available to store it. In ground guns, it is also unnecessary to pause while reloading, as in most cases the belt links are designed to allow a new length of belt to be clipped onto the end of the old one. These merits have made belt feeding by far the most common method used by the kind of heavy weapons described in this book; but there are also disadvantages which have led to the use of alternatives in certain circumstances.

The main problem in systems which use the guns action to drive the mechanism is that this places certain limitations on the arrangements for holding the belt. The gun cannot be expected to pull a heavy belt very far, and even in the best of circumstances the rate of fire of a belt-fed gun is likely to be lower than that of an equivalent magazine-fed weapon. There are also the problems in aircraft installations of disposing of the belt links and cartridge cases (the bulges underneath the nose of the Hawker Hunter jet fighter are containers for links), and in some cases of the belts jamming or even pulling apart under G forces. In the largest calibres of automatic weapons a belt would simply be too

A mm un it ion feed for aircraft wing mounting

Belt guides for M61A1 in gun pod (Courtesy: MoD Pattern Room)

M61a1 Hydraulic Drive

FEED CABLES

CABLE ACTUATING SPRINGS

MAGAZINE

MAGAZINE FOLLOWERS

M61 Ammunition Feed System

FEED CABLE

FEED CABLES

CABLE ACTUATING SPRINGS

MAGAZINE

MAGAZINE FOLLOWERS

Spring-Loaded Cable Makes U-Shaped Magazine Possible.

FEED CABLE

Mauser 30mm

Oerlikon linkless ammunition feed system for BK27 cannon

(Courtesy: Ian Hogg)

unwieldy although a variation in the form of a continuous-loop belt (i.e. forming an endless chain) was used in some aircraft installations such as the

USAAFs 37mm M4.

These difficulties have led to the development of linkless feeds for use with heavy automatic cannon or where very high rates of fire are required. These are often power-driven, the best examples being those for the rotary cannon used by most American aircraft. In most installations, the ammunition is arranged in a large helical drum, with the cartridges pointing inwards. The ammunition feed is driven by the same motor which powers the gun, ensuring that the cartridges are fed into the weapon at the appropriate rate. Because of the difficulty of disposing of empty cartridge cases from a supersonic aircraft, the ammunition feed slots the fired cases tidily back into the drum.

Magazine capacities for the fast-firing rotaries are necessarily high (exceeding 2,000 rounds in one M61 installation) which poses obvious problems in reloading. These have been tackled by the universal ammunition loading system (UALS) which is a mobile unit specifically designed to reload M61 guns (and remove the fired cases). It contains its own pneumatic drive and can reload a 515-round magazine in four minutes.

An alternative approach to reloading has been adopted for the 30mm M230 chain gun in the AH-64D Apache Longbow helicopter. The 'Sideloader' unit is a mechanical system built into the aircraft which enables one man to load 1,075 rounds, in eleven-round strips, in less than fifteen minutes. This contrasts with the AH-64A, which is reloaded by three men, using ground support equipment, in more than half an hour.

Ammunition feeding is complicated by the fact that the majority of heavy automatic weapons are designed to recoil in their mountings in order to spread out the recoil force and minimise vibration. A clip, or a box or small-drum magazine, can recoil with the gun, but it is not feasible to arrange this for belt-drives or other large ammunition capacity systems. It is therefore necessary for designers to find some way of transferring ammunition from a stationary supply to a moving gun.

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