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 an intermediate design before he produced his 'World Standard' design in 1887.
The majority of the text in this page is based on Hiram S. Maxim's paper 'Description of the Maxim Automatic Machine Gun' read before the Institution of Mechanical Engineers, and published in 'Engineering', Volume 39, June 5, 1885, pages 634-636 [Mx2]
Maxim Automatic Gun
Maxim conceived the idea of making a gun in which the recoil should be utilised for loading and firing in his early years; but it was not until 1883 that he had any time to devote to this problem. Before commencing experiments he considered carefully the different methods which might be employed for working an automatic gun by means of power derived from the burning powder. In those which he afterwards experimented upon, the power required was derived in the six following ways:
(1) Power derived from the gases escaping from the muzzle of the gun, either by utilising their pressure directly, or by employing them as an ejector to produce a vacuum in a chamber near the muzzle of the gun;
(2) power derived from the recoil of the entire gun;
(3) power derived from the recoil of the barrel, the breech-block, and the lock;
(4) power derived from a backward motion of the cartridge in the chamber at the instant of exploding;
(5) power derived from only a portion of the cartridge moving backwards;
(6) power derived from the elongation of the cartridge at the instant of exploding.
As Maxim was the first to make a gun of this kind, he had no data whatever to go upon, and had therefore to contrive some kind of device for ascertaining both the quantity and the character of the power to be dealt with. He constructed an apparatus to conduct experiments on a gun in which the power was derived according to the third of the above methods - namely, from the recoil of the barrel, the breech-block, and the lock.This apparatus consisted of two parallel steel bars, clamped into supports, and having the barrel and the breech-block mounted between them. The whole was so constructed that all of the parts were adjustable. The distance through which the barrel recoils before the breech-block becomes detached from it, was adjustable; the further distance that the barrel travels backwards, after it becomes detached from the block, was also adjustable; the travel given to the striker was adjustable; the angle at which the crank stood at the instant of explosion was adjustable; the amount of weight in the rotating parts and their distance from the centre of rotation were also adjustable.
This experimental apparatus was made as far as possible of soft steel and brass, in order that the action of the gunpowder might be observed upon the various parts. If any part showed signs of yielding under the strain, it was obvious that this part required strengthening in the gun ultimately to be made. The apparatus fired about a thousand cartridges, and at the end of the trials was still in firing condition. With one hand on the muzzle the barrel can be pushed back with sufficient force to perform the whole cycle of operations for firing, the push of the hand taking the place of the recoil of the barrel. In this way it has been found that a pressure of about 60 lb (27.2 Kg). travelling through a distance of 7/8 in (22.2mm). is the power required for working the gun, which is very much less than the actual power derived from the recoil, as determined approximately by Maxim in experiments with a Winchester rifle of the " express" pattern.
First Prototype Gun.
Having in this way determined the character and quantity of the power to be dealt with, and having ascertained the time required for the gas to escape from the barrel, as well as the strength required for the several parts, and the distance through which they had to travel, Maxim proceeded to make his first gun, the construction of which is shown in the accompanying drawings and images.
Naming the Parts
Description of Operation
Locking and unlocking breech to barrel
Breech is kicked away after unlocking
As breech moves back, the cartridge hook is lifted and shutter moves across (Rollover)
Cam causes intermittent rotation as it moves backwards and forwards (rollover)
Firing Rate control
The barrel is encased throughout the greater portion of its length within a water-jacket, which projects from the front end of the casing that encloses the machinery.
The barrel is able to move longitudinally within the gun frame. When the shot is fired, the barrel moves backwards due to the recoil. This recoil is initially opposed by a pair of flat springs, one at each side, which have to be forced apart by toggle struts recessed into the sides of the barrel. As soon as these struts have passed the centre, the springs close together again, accelerating the backward motion of the barrel.
During the first half of the 7/8 in. (22.2mm) backward travel of the barrel, the breech block is firmly locked to the barrel by a locking catch which is held firmly down by the crossbar. However, when the barrel has moved backward through 7/16 in. (11mm) the catch is released and raised by a projection on its forward end contacting the face of the cross bar. The breech is now unlocked from the barrel. It should be noted that in this time, the bullet has left the barrel and gas pressure in the barrel has dissipated.
The objective now is to drive the breech away from the barrel in order to retract the spent cartridge, and position the mechanism to load a fresh cartridge. A Straight lever, is pivoted on the barrel. At the same instant that the breech is unlocked from the barrel, one of the arms of the lever makes contact with a fixed Stop on the casing. The Straight lever pivots and the longer arm drives a Sliding Rod backwards with increasing force and rapidity to 'kick' the breech away from the barrel. This kick also serves to slow down the barrel during the remaining 7/16 in. of its backward motion.
The motion of the breech now carries the Crank over back centre, at which point the backward motion of the breech ceases, and it starts to move forward under momentum stored in the crank. Maxim notes that with freshly loaded cartridges the momentum given to the crank and its attachments is found sufficient to drive the breech-block forwards again into its firing position and to fire the next shot. But with old and weaker cartridges the gun is found to work with greater certainty if a strong Helical spring is used to assist in drawing the breech-block forwards again into its firing position after the crank has passed the back centre. Consequently all guns made after the very first experimental gun are now provided with this spring.
Extracting the Spent Cartridge
The Extractor is a forked lever attached to the rear of the barrel assembly. Once the breech block has been unlocked from the barrel, the lower legs of the Extractor come up against a transverse rod attached to the casing. The Extractor pivots, and the upper arms which lie just forward of the cartridge rim, force the cartridge backwards about 1/4 in out of the barrel. This is a powerful motion, and frees the cartridge which may be tight in the barrel chamber after the explosion of the powder charge. The extraction of the spent cartridge is then completed by a Cartridge hook attached to the same crosshead as the breech-block. The Cartridge hook is held down to engage with the cartridge rim by long fixed springs until the cartridge has been fully drawn into one of the pockets of the Magazine cylinder. Then the Cartridge hook is lifted as its arms rise up over a fixed crossbar to release the cartridge. The breech then continues on its rearward motion.
Rotating the Magazine Cylinder
Fresh cartridges are carried into position for loading by a Magazine cylinder. The Magazine is rotated intermittently through the motion of the breech. A cam on the bottom of the breech block engages with a spiral ratchet-wheel at the rear of the Magazine cylinder. As the breech reaches its rearmost position, the Magazine cylinder is rotated through 15 degrees, and on the forward stroke, through a further 15 degrees. This moves a fresh cartridge into line for loading, and at the same time rotates the spent cartridge out towards the ejection port.
Charging the Magazine
Ammunition is supplied in a canvas belt. The loading mechanism has to extract the cartridges from the belt and move them into position where they can be loaded into the barrel chamber by the forward motion of the breech.
The ammunition belt is carried on a flanged wheel so that each cartridge is held in an individual recess in the flanges. The casing around the flanged wheel has a number of alignment grooves, so that each cartridge rim is precisely positioned for extraction. This compensates for movement of the belt during firing and for variations in the position of cartridges in the loaded belt.
A Cartridge puller arm is attached to the foot of the breech assembly. During the forward stroke of the breech, this arm is carried into cutout outs in the flanged wheel, and a spring forces it up to engage with the rim of a cartridge in the belt. During the backward stroke the puller arm pulls the cartridge out of the belt and into the lowest pocket of the Magazine cylinder. The puller arm is then tripped downwards to leave the cartridge in the Magazine.
The Magazine cylinder is enclosed in a cover which holds the cartridges in place as they are rotated step by step into line for loading.
The empty belt passes out through an opening in the left-hand side of the gun casing; and through another opening on the same side the empty cartridges drop out, one by one, from the pockets of the Magazine as it rotates.
During the backward travel of the breech-block a Hinged Cover Plate is thrown across laterally over the magazine by the pressure of a coiled spring, in order to prevent any risk of the cartridge being jerked upwards out of the magazine.
Cocking the Gun
As the crank approaches the back centre, towards the end of the backward travel of the breech-block, the tail of the Cocking lever, which is pivoted upon the crosshead, comes against a fixed stud connected across the casing. In the remainder of the backward travel the cocking lever then compresses the main spring, which is a helical spring coiled round the striking pin; and a suitable catch or Sear also hinged upon the crosshead, finally catches the nose of the cocking lever, and holds the striker cocked in readiness for firing the next shot.
Loading and Firing
The second half of the cycle of operations, as the breech block travels forwards consists in pushing the fresh cartridge home into the barrel, locking the breech-piece, and releasing the sear Q for firing the shot.
As soon as the crank has passed the back centre, it begins to push the breech-block forwards and as described earlier, rotates a fresh cartridge into line in front of it. Near the end of its movement, the Crosshead comes up against the Sliding rod, which is protruding rearwards beyond the barrel. Further movement of the breech causes the sliding rod to press on the straight lever and thus starts to move the barrel forwards. Thus the barrel is moving before the breech block catches up with it, and therefore lessens the impact. As the barrel moves forward the Locking Catch is forced down by the Crossbar to lock breech and barrel together. The toggle struts, which have been forcing the flat springs outwards until this point, pass the centre and the springs urge the barrel and breech forwards . When the barrel and breech reach their forward-most position, the Sear lever coming into contact with the firing cam releases the firing pin, which fires the cartridge.
Firing Rate Control
Maxim's Prototype machine gun had a mechanism for regulating the rate of fire, from about 2-3 a minute up to 600 per minute. This mechanism used a hydraulic buffer to delay the final few millimeters of travel. The final movement of the barrel depends upon the rate at which water can be forced through a control valve. With the valve nearly closed, the barrel will take some time to move forward sufficiently so that the firing cam can trip the sear and fire the cartridge. With the valve open, the delay will be less, and so firing rate is increased. Note that the barrel is being forced forwards under the tension of both the Helical spring and the flat springs and toggle against the hydraulic buffer.
Firing/Rate control lever acts as the trigger. When the lever is set to safe, the gun cannot be fired, however, as the lever is pulled back the gun will start to fire (assuming there is a cartridge in the chamber) and the further the lever is pulled, the faster the firing rate. Once set the gun will continue firing as long as ammunition is supplied. It is clear, however, that this firing arrangement is not particularly safe, as the gunner has to reach past a rapidly moving crank to adjust or stop firing. The 'production' version of his prototype did not use the firing/rate control lever, using a simple firing lever at the rear of the gun. It is not known, however, if there was also a separate rate control provided.
The gun shown here is the size known as rifle calibre, which would doubtless be of great service in the field. It is 4 ft. 9 in. long over all, from the muzzle to the rear of the casing that contains the firing mechanism. It stands about 3 ft. high upon its tripod. The belt supplying the cartridges is made of two lengths of canvas, riveted together at regular intervals with brass eyelets and strips, so as to form a succession of loops, into each of which a cartridge is inserted by hand. When any belt is running out, a fresh one is hooked on to its tail end, without causing any delay to the continuous firing of the gun. The simple water jacket encasing the barrel of the gun is found to answer very well for preventing excessive heating of the barrel, as the amount of heat required to evaporate water is so very great.
The gun is mounted upon a tripod, which is a very convenient stand for exhibiting its working. The tripod of course is not a necessary part of the gun, the mounting of which depends altogether upon whether it is wanted in the field or on shipboard. The crank handle projecting at the rear from the right-hand side of the gun, is necessary in order to work the crank for bringing the first cartridge into the barrel of the gun; also for removing from the barrel any cartridge which may have failed to explode. The cartridges for supplying the gun are placed in a box beneath, which may be made large enough to contain almost any number. In a light field carriage about 2000 would be a fair supply; the box here shown holds 333, or one-sixth of that supply.
On introducing a belt of cartridges into the gun, and turning the crank handle, the cartridges are drawn in one by one, until the magazine is full, that is, until it is filled round half its circumference up to the barrel, and empty round the other half; and the empty part of the belt hangs out from the opposite side of the gun. Seven turns will draw seven cartridges out of the belt, and there will then be six cartridges in the magazine of the gun, and one in the barrel. On pulling the trigger by hand, the first one of these cartridges is fired; and the gun will then supply itself from the belt and continue firing automatically as long as there are any cartridges in the belt. The firing can be stopped after only a single cartridge has been fired, or after two, three, or any other number up to a whole volley has been fired; and the gun can be made to fire either slow or with great rapidity. It is the first shot alone that requires to be fired by hand, after which the firing goes on automatically until stopped.
Suppose that any of the cartridges supplied to the gun should hang fire. At the instant of the cartridge being struck the breech is closed, and there is no power to open it automatically except the power locked up in the cartridge itself. This power does not develop itself until the carriage itself explodes; consequently the breech does not open until after it has exploded, and the cartridge cannot be withdrawn in the act of exploding, as it can in other guns. Thus the serious trouble occurring with all other machine guns in cases of hang fire cannot here occur, being rendered impossible by the very principle upon which the gun is constructed.
The case of a cartridge entering the barrel and failing to go off at all may be exemplified by placing in the magazine of the gun two good cartridges, then a bad one, and then two good ones. As soon as the first cartridge is in the barrel and has been fired by pulling the trigger by hand, the gun will fire the second cartridge automatically, and will attempt to fire the third or bad cartridge, but will fail. The bad cartridge has then to be removed from the barrel by working the crank handle by hand; the fourth cartridge has, like the first, to be fired by hand; after which the gun will fire the fifth automatically. The whole operation of passing the bad cartridge will occupy about half a second.
Hence, if a cartridge hangs fire, the gun waits for it; if it fails to go off at all, it must be removed by hand, which is done in about half a second.
As the gun requires no external power for working it, being wholly self-contained, it may of course be turned freely in any direction while firing. For target practice, and for accurate shooting at long range, it is convenient to train it with screws, as in the case of other machine guns; and suitable adjusting screws are accordingly provided.
Suppose however that it be desired to give a quick adjustment as to elevation. For this purpose the clamping screw is slackened on the telescopic elevating strut, and in a second the required elevation is approximately given; after which the clamping screw is tightened up, and a final true adjustment is given in the ordinary manner by the fine regulating screw. Again, if it be desired to spread the fire horizontally between two given points, as across a bridge or a ford or a pass; or to take accurate aim in the daytime upon a part of the enemy's position where he is expected to be at work at night; in such case the horizontal adjustment towards the right-hand side is made with one adjustable stop, and towards the left-hand side with another. The two stops can be set so as to give any spread that is wished, and to give it in any position desired. When so adjusted the gun can remain in this position till wanted, and can be fired in the night or at any other time with the certainty of covering everything between these two points without getting out of adjustment. For receiving cavalry or a sudden charge, the gun is clamped in elevation, but is left free to be moved completely round horizontally. For firing upon a quickly moving torpedo boat, it is wholly unclamped so as to be moved freely in all directions. [Mx2]
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