Generally with the revolving cannon, a regular cast-iron explosive shell with a percussion fuze was used; sometimes in the Navy, where a maximum of punching power was required, hardened pointed steel shot would be used. For protecting (flanking) the dry ditches of fortifications, and for which a particular pattern of gun was designed, canister shot was used.
Steel Shot with Base Fuze (full size 1024 x 768 136Kb)
Common Shell (full size 1024 x 768 144Kb)
40mm Case Shot for Flanking Gun (full size 1024 x 768 128Kb)
Case Shot (full size 1024 x 768 128Kb)
The common shell was made of cast iron with a quantity of gunpowder and a nose fuze. A soft brass band was pressed around the iron shell which would grip the rifling when fired, so imparting the necessary spin to the shell to stabilise it in flight.
Shells were designed to explode on impact, and to distribute a large number of lethal fragments to cause the maximum damage to men and material. The 37 mm Hotchkiss shell would generally break up into 16 - 20 fragments, so that the Hotchkiss supporters would claim one shell was the equivalent of 16 solid bullets fired from a competitor design.
Two types of fuzes were fitted - the land service ammunition was fitted with the Hotchkiss percussion fuze, a very safe fuze which was used well into the 20th Century, while the naval service shells were generally fitted with the Desmarest fuze. Both are described below.
The explosive shell was preferred by most countries that bought Hotchkiss revolving cannon. It had the advantage that the explosions could be seen, so the gunner would know where the shells were landing and could adjust his aim. It was not easy to know if solid bullets were hitting their mark especially at the longer ranges.
As torpedo-boats increased in size, they became better protected, with thicker steel plates and coal bunkers to protect the vital areas, generally taken to be the boilers and engines. The common shell did not have the penetrating power to pierce the steel plates, so steel shot was employed. These shot had a sharpened point and were mostly tempered and hardened steel with a very small amount of gunpowder, to be triggered by a base fuze (see below).
During the 1880's torpedoes had an effective range of about 500 m, and trials conducted against representative targets were correspondingly short. Steel shot would penetrate about 35mm of steel from a range of about 250 m if the shell struck normal to the plate, or about 13 mm at an impact angle of 60 degrees. This was thought adequate in 1885.
Naval tactics in the 1880s were firmly based on close range encounters, indeed ramming had been seen at the principal means of destroying an enemy fleet following the battle of Lissa. Taking a ship by boarding was still a valid tactic, and weapons - cutlasses, pistols and rifles were provided throughout each warship for the crew to board or repel boarders. Every man on board had an assigned weapon for boarding.
Therefore, there was a need for guns to be able to sweep away the mass of boarders at short range, as had been done from Trafalgar and before, by loading cannon with cases containing a large number of bullets. These could be fired from a Hotchkiss revolving cannon at a rate of up to 60 rounds per minute, and would provide devastating hail of lead at short range against anyone exposed on an opposing ship.
The 37 mm case shot round was a thin drawn brass case filled with 28 hardened lead balls of 19 grams each. The 47mm and 53mm guns fired 30 and 58 balls respectively, each nearly 30 grams in weight. The balls were embedded in sawdust to stop them moving.
In land service, however, the use of case shot was more important, to sweep away the massed ranks of troops at short ranges.
The Flank-defence gun was designed to provide a hail of lead balls across the ditches surrounding French forts. Flank-defence Hotchkiss guns had a calibre of 40mm and fired special case shots containing 24 hardened lead balls weighing 32 grams each. Flank defence guns had different rifling in each of the five barrels, which caused a different spread to the balls, and therefore could cover an entire ditch from close in to far away without the need for aiming the gun.
Creating Coiled Brass Cartridges
37mm Solid Drawn Brass Cartridges (Royal Armouries)
In 1880, the cartridges for all calibres of this gun were made of a trapezoidal piece of sheet brass, wrapped, strengthened at the base by two or more reinforcing cups, the whole riveted together, with the head made of sheet iron. In the base there was an ordinary primer in a detachable case, which looks like a little pistol cartridge. These cartridges could be reformed and used about eight times over. The animation gives an idea of how these coiled cartridges were formed.
Solid-drawn cartridges, especially the larger calibres, were liable to stick in the gun, which made it difficult to extract them. There was a significant risk that the head could be ripped off The coiled cartridge, being spirally rolled, would open out a little, by the pressure of the powder, and mould itself to the chamber to prevent the escape of gasses, but would spring back again so that it was very easy to extract a cartridge after it has been fired.
However, by 1880 cartridge manufacturers, particularly in America, were perfecting the brass alloy used in drawn-metal cases, using very pure copper and annealing the cartridge after forming. This was highly effective for the smaller cartridges used in the Gatling and Gardner machine-guns, and by 1885, the technology and metallurgy had advanced sufficiently to manufacture drawn-metal cases for Hotchkiss ammunition. These cartridges were ductile enough to expand to seal the breech, but contracted to their former size afterwards to prevent them sticking in the breech.
The optimum weight for a 37 mm projectile should be about 1 kg (2 lbs) with a muzzle velocity of about 500 m/s (1,600 to 1,700 ft / sec). However, the French Naval artillerists requirements were for a gun that should not exceed 200 kilograms in weight; it should be possible to put it in the fighting tops; it should be short, have no projecting parts to it, and minimum recoil. In a gun limited to about 200 kg (400 lbs.) weight, if you fire large charges and large projectiles with high velocities, the recoil on the man would be so violent that he would not be able to withstand it, and for that reason Hotchkiss was obliged to cut down its power. But the smaller projectile and reduced charge gave ballistical results better than were even asked for by the French Navy.
The development of the ammunition can be seen from the published literature. In 1874, the 37mm revolving cannon was the fore-runner of the Heavy field gun, having 1276 mm barrels (50.1 inches) and firing a 520 gram shell with a bursting charge of 25 grams of gunpowder. The powder charge was 120 grams of gunpowder. This gun proved to be too heavy for naval use, and the recoil too violent. By 1879, the Heavy field service 37mm revolving cannon ammunition had reduced the propellant from 120 grams to 110 grams and the shell weight increased to 525 grams. The Heavy field service gun weighed 475 Kg, so a light service gun was introduced weighing 225 Kg. This lighter gun required a smaller projectile and smaller propellant - 455 grams, 22 grams of gunpowder for bursting charge and 80 grams of French Ripault powder giving a range of about 4,200 m and muzzle velocity of 402 m/s (1,320 ft/sec). The light field model was the model used on ships.
Hotchkiss Base Fuze Operation
Hotchkiss Base Fuze (full size 1024x768 188Kb)
Hotchkiss Nose Fuze (full size 1024x768 164Kb)
Hotchkiss Nose Fuze Operation
Desmarest Fuze (full size 1024x768 176 Kb)
Desmarest Fuze Operation
Hotchkiss Base fuze for steel shot
The Hotchkiss Base Fuze consists of three main parts, the body, the plunger and the detonating cap. The body is made of gun-metal.
The plunger is composed of a block of lead cast into a cylindrical brass base, and holds a rough wire firing pin, roughened so as to grip the surrounding lead. The lower end of this firing pin projects below the bottom of the plunger, whilst its front end is sunk a little below the front surface, which is hollowed to leave it clear. On assembly, the lower part of the firing pin rests on the floor of the body chamber, while the top rests against the lower surface of the cap, thus holding the plunger steady.
When the gun is fired, the inertia of the plunger drives it to the rear along the brass wire, the lead setting up and gripping the wire firmly. The point of the firing pin protrudes above the lip on the plunger, and the fuze is now armed. On the projectile striking any object, the plunger drives forward, the point of the wire detonating the composition in the cap, which drives its flame through the vent in the top of the fuze.
The Hotchkiss Nose-Fuze consists of four parts, the body, the safety plug, the plunger, and the head. The body is made of brass, and has a strong shoulder at the upper end for securing in the shell. The outside of the shoulder is shaped the the ogive.
The plunger is a brass hollow cylinder with a lead lining to give it weight. In the centre is a chamber (magazine) filled with gunpowder with a percussion (fulminate) cap over it. A small brass wire loop is moulded into the plunger so that its two ends project down through the base of the body.
The safety plug is a lead stopper forced tightly into the hole in the bottom of the body, and by pinching the brass wire, holds the plunger steady.
When the shell is fired, the plunger is forced to the rear, driving the safety plug out into the shell. The small wires being free to let the plunger drive forward, hold it steady with the rotation of the shell, and keep it from dropping forward on the descending arc of a high trajectory. On impact the plunger drives forward and the percussion cap explodes the little internal magazine which sets off the main charge.
The Hotchkiss Nose-Fuze was used in Land-service ammunition. It was a particularly safe fuze, and was used well into the early 1900s. Unlike the Desmarest fuze, it would explode on a graze, as well as a direct hit.
The Desmarest Nose-Fuze has the merit of simplicity of construction, although, as it is intended to act by direct impact, it is unreliable on graze. It consists of a gun-metal body which screws into the shell and has a shoulder shaped to the ogive. In the base of the chamber of this body a percussion cap is placed, mouth down.
A plunger made of light wood has an iron striking wire fixed in its base, and this is pressed tightly into the open nose of the fuze, and is held secure by two brass suspending wires.
The nose of the fuze is made watertight by putty.
When the shell is fired, the plunger, being very light and held in position by the brass wires, is sufficiently supported against the shock of discharge, and remains in place.
The fuze acts on direct impact, the plunger being driven down and thus exploding the cap.
Common shell and steel shot for the Hotchkiss 37 mm light gun. (G Spragge)
Three calibres of common shell, two case shot and three calibres of steel shot