Improvements in Battery-Guns.
For the second model of his 1862 gun, Richard Gatling had used metallic cartridges in place of the paper cartridges issued as standard to the infantry. However, the cartridges were still loaded into strong steel cartridge chambers which had to be hand loaded before use, and which, when fired, might not be aligned precisely with the barrel causing inaccurate fire. There would also be a significant escape of gas as the cartridge chamber was only pushed up against the rear of the barrel.
Gatling realised, in his second gun patent of 1865, that he could adapt his mechanism for continuously loading and firing to exploit the improved metallic cartridges that were beginning to be manufactured at the end of the American Civil war.
The major problem with all breech loading firearms is how to seal the breech to stop the explosive gasses leaking backward. These hot gasses will damage the breech and threaten the firer, not to mention the lessening the pressure behind the bullet so range is decreased. A metallic cartridge is designed so it will expand slightly when fired so the walls of the cartridge fit tight against the inside of the breech chamber, thus stopping the gasses from leaking back (a process known as obturation). However, the metal must then contract enough to allow the empty cartridge to be pulled out. If the metal is permanently deformed, the cartridge will stick, and there is a risk that the cartridge rim will be pulled off. This is more likely with the built-up cartridges such as the English Boxer.
It was found that the copper mined in the Lake Superior region was particularly pure and could be made into brass that had the necessary strength and ductility to be made into effective cartridges. American manufacturing techniques had perfected a process of drawing and regularly annealing the brass blanks to give cartridges of exceptional quality.
Given the reliability of the cartridges that were being manufactured, Gatling's 1865 model gun was arranged to load, fire and extract the spent cartridges in a continuous process.
The 1865 model fired the then-standard .58 rim-fire metallic cartridge, which was supplied in cases containing about 22 rounds. The U.S. Government was favourably impressed with this model and ordered over a hundred for the Army and Navy (the Model 1866), to fire either a 1 inch round or the new .5 inch 50-70 cartridge.
Richard J Gating's first Gatling gun had very limited use during the American Civil war. However, by 1865, he had refined his design to exploit the improved quality and availability of metallic cartridges. The U.S. Government tested his prototype and ordered 45 guns to fire the .5 inch 50-70 cartridge, and 61 to fire a 1 inch cartridge. These guns were designated the model 1866 but were built to Gatling's 1865 design. This page shows how the 1865 gun worked.
Animation of Gatling Gun 1865 Patent [G5]
The Parts of the Gatling Gun, 1865 model. Mouse over to view original Patent drawings [G5].
How it Worked.
As in his previous model, Gatling wrapped a number (6 in this case) of complete rifles around a common axis. Each rifle consisted of a barrel, a cartridge cavity and a lock which can be made to oscillate backwards and forwards to load a cartridge, fire it and then retract the spent case.
The locks are carried in a lock cylinder which is keyed on the same shaft that carries the barrel assembly and cartridge carrier, so that the locks are always perfectly aligned to their respective barrels. The whole assembly is rotated by handle driving a pinion that engages with a cog wheel on the gun axis.
Each lock consists of a plunger, made up of a butt piece, into which is screwed a solid shaft which is connected to a flange and the breech-pin. The firing hammer is a sleeve with a lug, and is mounted on the shaft where it can be forced forwards by a coil spring. As the plunger moves forward, the breech pin forces the cartridge into the rifle's breech and holds it there when that cartridge is fired by the punch. The punch consists of a collar that can move feebly on the plunger's shaft, and a punch arm that is set into the breech pin. As the cartridge is forced into the rifle's breech, the punch is pushed back leaving a small gap between the collar of the punch and the plunger's flange. When the hammer is released, it strikes the punch collar, forcing it forward. The impact causes the punch, which had rested on the rim of the cartridge, to compress the rim of the cartridge and explodes the fulminate within the cartridge rim to ignite the bullet's charge.
As the whole assembly is rotated by the gearing, one of the hollows in the cartridge carrier passes under a cartridge box and pick up a fresh cartridge. At this point the lock is fully withdrawn in the lock cylinder. The assembly continues to rotate and the butt piece of the plunger starts to ride up on the rear cam inclined plane (shown in green), so forcing the lock forwards, and with it the cartridge. As the plunger moves forwards it carries the sleeve-hammer with it until the lug of the hammer comes into contact with the rear face of the stationary cocking cam (shown in blue). The hammer is now forced back so compressing the spring while at the same time the plunger is forced forwards by the inclined plane cam.
Immediately prior to firing the butt piece reaches a flat portion of the cam, and at this point the plunger has pushed the cartridge fully into the chamber of its rifle barrel. The punch, which normally extends a little beyond the end of the plunger has been pushed back a small way, leaving a small space between the collar of the punch and the flange of the plunger.
With the barrel at the 6 o'clock position, the cocking cam is abruptly cut away, and this allows the hammer sleeve to be driven forwards by the spring. The hammer hits the punch collar driving it forwards and pinching the rim flange of the cartridge, which is thereby ignited.
The flat portion of the rear cam continues a little past the 6 o'clock position to keep the lock in place as a precaution against a hang-fire. The recoil force of the discharge is carried through the plunger and butt piece to the solid rear cam.
As the assembly rotates further, the lug on the rear end of the butt piece comes up against the retracting cam-surface (shown in red), and the plunger is pulled back bringing with it the spent cartridge, which is allowed to fall clear of the cavity of the cartridge carrier.
With the hindsight of many years we can see two major design weaknesses of the 1865 design.
The first is the the punch which makes contact with the cartridge rim at an early stage in the cycle, but is only kicked forward when the hammer is released. At high firing rates and when the lock plungers become fouled, it is possible for the punch to become so stiff that it ignites the cartridge when it first comes into contact with it. This causes a premature ignition - the cartridge is not fully into the protection of the rifle's breech. Later designs of Gatling gun ensured that the firing pin or punch was held back until the desired moment of ignition.
The second design weakness is in the adjustment of the 'headspace'. When the gun is set up, the length of each plunger is adjusted so that there is no slack between the rear of the cartridge and the solid rear cam. However, as firing continues, the metal of the gun expands resulting in the plunger not being as tight up against the breech as desired with resultant loss of range and potential damage to the gun. The 1865 gun includes a screw at the forward end of the frame to make adjustments to the headspace - the space between the plunger and the chambered cartridge. However, to make the adjustments, a gunner has to stand at the front of the gun, which has several of its rifle barrels loaded, and screw the assembly closer together. This had, on occasion, the result that one rifle was discharged, causing injury to the gunner. It was not until the 1880s that this problem was finally solved.
Notes on Gatling's Patent No. 47,631
Gatling patent shows a 4-barrel gun, although he is at pains to point out that his mechanism can be made with a different number of barrels. There is no record that a 4-barrel gun was ever built; instead 6-barrel guns were manufactured, and I have shown this in my animation.
Gatling's patent specified a casing around the barrels which would hold water, plaster-of-Paris (!) or other material to preserve the barrels from 'injurious expansion' by excessive heating. This casing is labelled the water jacket in the diagram above and is shown in the animation. However, none of the contemporary drawing of 1865 guns nor existing examples have this casing, so it appears to have been dropped in the production models.
If you are unable to view this Quicktime movie, click here to view the animation on YouTube