The first automatic machine gun was invented by Hiram S. Maxim in 1884. Prior to Maxim’s invention, machine guns were operated by hand – either by turning a crank or moving a lever. In Maxim’s gun the operations of loading, cocking, firing, withdrawing the empty cartridge from the barrel and ejecting it are performed by the recoil energy resulting from the explosion of the cartridge. This page describes his first prototype gun. Maxim refined his design, simplifying and improving the mechanism in a second prototype and a transitional design before he produced his 'World Standard' design in 1888.

Maxim's Second Prototype Automatic Machine Gun, 1885

Hiram Maxim's second prototype machine gun, from patent No 1307 of 1885. Maxim was continually improving his designs. He was looking to simplify and reduce manufacturing costs as well as improve the reliability and performance of his machine guns. Following on from the success of his first prototype, which attracted large number of the affluent and influential 'society' of London, Maxim submitted a provisional specification patent on 29 January 1885. This web page looks at that design, and the innovations that it introduced. More importantly, by the time the full specifications for Patent 1307 of 1885 were approved in 29 October 1885, Hiram Maxim had included some alternative modifications that appear in all later forms of his gun.

The animation shows the operation of the gun described in Maxim's full specification of January 1885. Although it is probable that Maxim made examples of this gun, it never entered production and no examples exist to my knowledge. However, these patents show the evolution of Maxim guns from the earliest prototype to the World Standard Model of 1895, and beyond.

Maxim's first prototype was highly effective in demonstrating the effectiveness of automatic fire, but he was advised that to be accepted by the military, his gun needed to be simple enough to be stripped in the field without tools and light enough to be transported over rough terraine. In his second prototype design, Maxim produced a gun that could be easily dismantled, was lighter and mechanically simpler than the first prototype.

The Innovations

As in his first prototype, Maxim uses the recoil force to extract the empty cartridge case, cock the firing mechanism, load and then fire the next round. Maxim ensures that the barrel and the breech remain locked together for the first part of the recoil movement; in the first prototype the was done using a catch that was released after the barrel and breech had moved a set distance to the rear. In the second prototype, Maxim uses a crank arm to lock the barrel and breech together. While the crank is in-line with the breech, the breech is held tight against the rear of the barrel. However, once the crank is rotated slightly, the breech is released and moves rapidly backwards. It is the movement of the breech unit that effects the extraction and loading of the ammunition, and for operating the feed mechanism. This type of 'knee' joint lock is also to be found in other weapons of the period, e.g. Smith & Wesson Volcanic, Luger, Borchardt.

Naming the Parts

Overview of Operation

 

We will start at the moment the firing pin is released and the cartridge ignited. The recoil acts through the breech and the crank arm to move the inner frame to the rear. After a short movement, an arm attached to the crank hits a 'resistance' piece on the outer frame, which starts the crank arm to rotate thus breaking the lock and the breech starts to move rapidly to the rear and in doing so drives the crank through 180 degrees rotation. In the first part of its rotation, the crank arm re-cocks the firing pin. As the breech moves to the rear, an upper arm attached to it pulls a fresh cartridge from the ammunition feed belt into a feed wheel chamber, while at the same time an extractor hook on the bottom of the breech pulls the empty cartridge case into the lowest chamber of the feed wheel. Then at the rearmost extent of travel, a cam on the breech causes the feed hopper to rotate to present a fresh cartridge behind the barrel. The breech then starts to move forward due to the pressure of the main spring, and as it does so pushes the fresh cartridge into the barrel. The breech is also linked to a moving tray which forces the ammunition belt through the feed tunnel so that the upper arm can hook over a fresh cartridge.

The principle is that the centre of rotation of the crank that holds the breech in place is slightly above the centre line of the barrel and breech. Consequently when the cartridge is ignited, the recoil force tries to turn the crank in the 'Up' direction, but as the link cannot rotate the crank is locked in position, holding the breech firmly against the rear of the barrel. However, if the crank can be rotated through an external means, the forces now apply below the crank's centre of rotation, causing the crank to rotate rapidly in the down direction due to the recoil force.

 

Firing pin release

There are two sears that must be disengaged before the firing pin can be released to fire the next shot. One sear is disengaged as the crank arm moves into line with the breech and into the 'locked' position. In addition to automating the firing, this is also a safety feature to ensure the gun cannot be fired unless the crank is locked behind the breech, The second sear is disengaged by the gunner pulling the trigger. So long as the trigger is kept pulled, the gun will fire continuously as long as ammunition is supplied to it, but the gun stops shooting the instant the trigger is released.

The firing pin is held in its cocked position by a shoulder caught behind a block fixed to the breech. As the crank arm returns to its locked position, it lifts the rear of the firing pin so that the shoulder is clear of the block. The firing pin is now free to be driven forward by the firing spring, but only if the trigger is pulled to release the other sear. These rollovers illustrate the mechanisms: in the first the crank arm returns to the lock position, and in its final degrees of rotation lifts the end of the firing pin clear of the shoulder. In the second rollover, you will see the firing pin being pulled to release the firing spring sear. The firing pin can only drive forwards once both the crank is in the locked position and the trigger is pulled.

Re-cocking the firing pin takes place automatically as the crank begins to rotate; it sweeps the tail of the firing lever down so retracting the firing pin far enough that the shoulder again catches behind the block. A leaf spring above the firing pin ensures that the upper sear is held in this position. As the breech moves to the rear, the trigger sear rotates to lock the firing lever, and the mechanism is then ready to fire the next round.

Trigger catches

Maxim describes a set of levers that can be used to:

a. lock the trigger so that it cannot be pulled

b. lock the trigger in the fire position, so that the gun will continue to fire as long as ammunition is available

c. Allow the trigger to be pulled, and then hold the trigger in the fire position.

Modifications.

In the 9 months between the Provisional Specification and the Complete Specification, Maxim added additional designs to his Patent No. A.D. 1885 No. 1307. This was a common feature of Maxim patents. Maxim recognised that he was the first inventor to produce a fully automatic machine gun - one that use the energy from the explosion of the cartridge propellent to do useful work of extracting, reloading, cocking and then firing a fresh round. Consequently over the years from 1883 to 1890 and beyond, Maxim patented every possible design for a gun using either the recoil or the pressure from the burning propellent. By patenting all imaginable alternative mechanisms, Maxim hoped to prevent competitors from exploiting minor alternatives and thereby attacking his market share (although this was ineffective against Robert Brownings machine gun)

The significant alternative designs covered in Patent 1307 were:

a. a much lighted inner frame, with the outer frame now completely enclosed.

b. a spiral main spring with a chain attached to a profiled arm connected to the crank. This is the forerunner to the familiar 'fusee spring'.

c. The barrel now moves with the inner frame, while the cooling water jacked it fixed to the frame

d. The 'Resistance' now takes the form of a leaf spring instead of a shaped block

e. The moving tray is connected by a link to the inner frame, and not the breech. This permits a much simpler mechanism for feeding the cartridge belt through the feed tunnel.

f. A different firing rate control mechanism mechanism is proposed.