As the size of torpedo boats increased, more powerful guns were required to penetrate the plating to make a fatal hit. There was also a need to fire exploding shells - the 1" guns were restricted to solid shot. In the early 1880s Nordenfelt developed a series of single barrel guns that could be loaded and fired rapidly with minimal crew. The gun shown here is the 6 pdr on a recoil mounting (circa 1883) firing a 2.2 inch shell weighing 6 pounds. The gun illustrates Nordenfelt's Third system.
This single-barrel Nordenfelt shell gun fired a 2.2 inch diameter shell weighing 6 pounds to an effective range of 4,000 yards. Firing rate was about 12 aimed shots per minute, a great advance on other breech loading guns which had a firing rate of 2 per minute. This was achieved by use of ammunition that included the projectile, the powder charge and the means of ignition as a single item - the Quick Firing cartridge. Perviously shell, powder bag and igniter had to be loaded separately.
Handle and action cam. The extractor lever cam is to the right of the shaft.
Breech block, firing pin, trigger and main spring
Two views of the wedge. The machined teeth are shown in blue
Extractor, with extractor lever on left.
Recoil mounting for 6 pdr (circa 1884) (rollover)
Operation of Mechanism
Recoil mounting for 6 pdr (Gunnery Manual 1885)
Although Nordenfelt, in 1884 had seven different calibres of shell gun, ranging from 1.65 inches to 2.45 inches, they all used the same mechanism for loading, securing the breech and firing. I will concentrate on the model purchased by the Royal Navy in that period – the 2.2 inch ‘6 pounder’ heavy quick firing gun.
The principal parts of the mechanism are:
The firing handle operates through a 1/3-circle motion from front to back. It is connected to the main axis shaft.
The action cam is connected to the main axis shaft, and has a slot cut into it. Part of the slot is straight (or nearly so) and the remainder is an arc centred on the main axis. On its rear upper part is shaped to form a bearing surface that will act upon the trigger.
The breech block is made of steel, and carries the firing pin, spring and trigger. It has a falling motion to the rear when opened. The firing pin has bevelled projections or cocking lugs on its base for the wedge to act on, and on its under part in the centre is a lug by which the trigger retains it. The firing spring is a flat one of great power and strength. The trigger, of steel, is free to rotate on its retaining pins. On the arm of the trigger are two lugs, one above and one below – the upper lug is acted upon by the wedge and the lower by the action cam.
The wedge, also made of steel, has a vertical motion in the breech block. On its lower end is a pin which fits through the slot in the action cam.
The extractor lever is connected by a shaft to the double extractor, which works on both sides of the cartridge. The extractor lever is operated by an extractor cam lever which is connected rigidly to the main axis shaft.
The action of the mechanism is as follows, assuming the gun to have just been fired.
Handle Drawn Back
First The handle carries the action cam slot over the wedge stud in the part which is concentric with the main axis, and therefore no motion of the internal mechanism takes place.
Second Further rotation of the handle causes the straight part of the action cam to engage with the wedge pin, and the wedge is forced vertically downwards. As the wedge descends, machined surfaces (teeth - shown in blue) act on the bevelled projections of the firing pin, which is forced backwards and compresses the firing spring. When the firing pin lug is clear of the trigger, the wedge bears on the upper trigger lug, forcing up the trigger which catches and retains the firing pin. The gun is now cocked in preparation for the next cartridge.
At the same time, the extractor cam lever presses against the extractor lever, and causes it to rotate slowly, thereby starting to ease the cartridge out of the chamber.
Third When the wedge pin reaches the end of the straight part of the action cam slot, the handle, which is still being moved to the rear, causes the breech and wedge assembly to fall to the rear, rotating about the main axis. When the breech has been rotated out on the way, the extraction cam lever forces the extraction lever rapidly to the rear, and thus throws the empty cartridge clear of the breech block.
Handle Pushed Forward
A fresh cartridge round is pushed into the breech. This will come up against the hooks on the extractor, and will not be fully home.
First The handle is pushed forwards, and this rotates the breech and wedge assembly back towards the closed position, and in doing so pushed the fresh cartridge fully into the barrel.
Second The cartridge being fully home, the breech and wedge unable to rotate any further. However the handle continues to be moved forward, and the action cam continues to rotate. As it does so, the wedge pin is forced upwards in the straight part of the action cam slot, and the wedge is raised into position to lock the breech in position prior to firing.
Third The handle continues to move, and the curved part of the action cam moves around the stationary wedge pin. The action cam now presses against the lower lug on the trigger, pushing the trigger up and so releasing the firing pin and thus firing the gun.
The machined teeth on the inside of the wedge, which draw the firing pin back when the wedge descends, also prevent the firing pin from striking the cap of a cartridge until the wedge is fully raised and supported by the entire bearing surface. If by accident the trigger is pulled too early, the cocking lugs on the firing pin strike the wedge teeth and the point of the firing pin cannot reach the cartridge cap.
Simplicity of Mechanism
The entire mechanism consists of 10 pieces only. There is but one spring – the flat mainspring, and there are no cog-wheels or delicate parts. The entire mechanism can be taken out of the gun by hand without any tools by simply withdrawing the firing handle.
The drill stop, a lever at the rear of the breech on the right hand side, can be moved to four positions. In the first position, fully to the rear, a wedge is positioned so that it stops the final movement of the handle (the extension that acts against the drill stop is coloured red in the animation), which would cause the action cam to press against the trigger and thus fire the gun. In position 1 the gun is fired by pulling on the trigger, and this position would be used for deliberate aimed shots.
In the second position, the gun will be fired automatically when the handle is moved full forwards. This position would be used for rapid fire.
The third position is used when dismantling the mechanism, and the fourth to remove the drill stop lever itself.
The rifle-calibre, 1" Nordenfelt machine guns and the smaller shell guns can be mounted on rigid pedestals since the recoil can be absorbed without risk of damage to the ship’s structure. With the larger calibre, 2 inches or more, the mountings require to allow a certain amount of recoil so as to reduce the strain on the deck.
The main animation above shows a 6 pdr (2.2") shell gun on a recoil mounting from 1884. By 1885 the mounting had been revised to replace the front and side braces by solid side plates, however, the recoil action is better illustrated by the 1884 design.
The gun is mounted on a lever which is fork shaped with the trunnions bearings at the ends. The lever is pivoted on a central bolt which passes through the three supports (two side and one front) which are themselves connected to the mounting framework.
The lower end of the fork is connected to the piston of a combined hydraulic and spring buffer.
Another fork is connected between the pivot bolt and the elevating gear and this carries a lever connected to the breech block of the gun. These items are designed so that when the gun is fired its movement during the recoil backwards is exactly parallel to what the centre of the gun was before it was fired.
The elevation is controlled by a vertical hand wheel working a single elevating screw and training is given by a horizontal hand wheel, which works a cog wheel gearing into a horizontal toothed racer attached to the deck.
After recoiling the gun instantly returns to the firing position under the action of the recoil spring, and without causing any alteration in the training and elevation gear, the gun moving parallel to its centre line without throwing up its muzzle. This allows the gun to be fired rapidly since it does not have to be relaid between each shot.
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