If you are interested in an in-depth review of the various designs of the early automatic pistols this excerpt from Textbook of Automatic Pistols by R.K. Wilson is very detailed.
Textbook of Automatic Pistols
Automatic arms depend upon the principle of applying some of the energy produced in firing a first cartridge to prepare for the discharge of the next, and so on so long as further cartridges are supplied. This principle may be defined as follows: Part of the energy liberated by the combustion of the propellant is made use of to extract and eject the fired case, to cock the firing mechanism, and to feed a fresh cartridge into the chamber. In the case of self-loading arms the cycle of operations stops at this point, as a separate trigger pressure is required to fire each shot; but in fully automatic weapons the discharge of succeeding rounds is carried out without the necessity for this. The amount of energy required for these operations is comparatively small; indeed the chief problem of designers has always been how to dispose of the surplus upon their hands; in effect how to regulate matters so that the work of extraction, ejection, recocking and reloading shall be carded out efficiently and reliably, yet without undue shock and violence, which leads to breakages and increases disturbance of aim.
- The necessary energy is derived from the expansion of the propellant gases, and, generally speaking, it may be said that this power is utilized either-
(1) Directly: by allowing the expanding gases to come in contact with a reciprocating portion of the mechanism, or
( 2) Indirectly: through the medium of recoil.
The various systems of operation, for all automatic weapons, may be classified as follows:
(1) DIRECT OPERATION BY GAS.
(2) GAS PRESSURE LOADS UP SPRINGS WHICH WORK THE ACTION.
(3) OPERATION BY RECOIL.
(4) OPERATION BY A COMBINATION OF (1) AND (3).
- Direct Operation by Gas. This system of operation may be effected in two ways:
- By diverting a small portion of the gas through a vent in the barrel into a chamber or cylinder and allowing it to expand against a piston.
Hotchkiss, Lewis, Light Browning, Dame machine-guns, Clair pistol.
In the case of the Colt machine-gun, a pivoted radial lever is blown off a gas-port in the barrel.
- By trapping a portion of the gas in a small expansion chamber at the muzzle and allowing it to carry forward a sleeve; i.e., by utilizing the “muzzle-blast”.
Bang Self-Loading Rifle, Mclean pistol.
In both cases a reciprocating motion is obtained to work the action directly.
Gas operation by direct trapping through a port in the barrel has been very successful with machine-guns, particularly with the heavier types where plenty of weight can be allowed to the piston and reciprocating parts. In all guns worked on this system the gas must be trapped off the barrel at a very high pressure; in the case of a machine-gun firing service ammunition such as the American M.1 cartridge it varies from 20 to 5 tons per sq. in., depending upon the distance from the chamber at which the port is located. Moreover, this pressure only endures for about ½_000th of a second; so the result is a very sharp and violent blow to the piston and reciprocating mechanism; the breech-block would be slammed violently open, causing separated cases and frequent breakages of the action. In gas-operated machine-guns these difficulties have been got over very successfully by-
(1) Locating the port as near the muzzle as possible, where the gas pressure is in the neighborhood of 5 tons per sq. in., and
(2) Increasing the weight and consequent inertia of the piston and reciprocating gear so that the sudden blow is converted into a steady “push” which will continue to work the action against the load of the return-spring an appreciable time after the pressure on the piston has gone.
In practice it is very easy, with gas-operated guns, to arrange for the correct amount of power to be applied, provided the barrel is of reasonable length and the overall weight of the gun will allow for a heavy piston.
It will be seen that these essential conditions for successful gas operation are utterly impossible in any pistol both on account of weight and length of barrel, even allowing for the very much lower pressures developed by normal pistol ammunition. They also militate against the use of this system for self-loading rifles where a military cartridge must be fired from an arm weighing no more than the standard Service Rifle (8-9 lbs.), on account of weight, though a number have been made from time to time on this system, such as the Mondragon, and the French Self-Loading Rifles of 1917 and 1919. In 1910 a gas-operated sporting rifle was produced by the Standard
Arms Co. in America. It took the Remington .32 and .35 cartridges, but was not a success.
The “muzzle-blast” system has been developed with some success for self-loading rifles, both in the form where a sleeve of slightly larger diameter than the bore is carried forward by the expanding gas, and that in which a light piston lies below a comparatively large port. in an expansion chamber at the muzzle. This second method of operation is used in the Garand, which is probably one of the best military self-loading rifles yet produced. The system has many important advantages, notably the utilization of the gas at a comparatively low pressure and the absence of a port in the barrel itself with all the difficulties of erosion and consequent short life of the latter. The “muzzle-blast system” has not been seriously applied to pistols; there is the Mclean,38 of which I doubt whether any but a few experimental models were made; while Bang’s original specification, really for rifles, states that the invention may also be applied to pistols.
- Direct gas pressure on a piston which loads up operating springs. This system is an attempt to get over the difficulties inherent in gas-operated guns of the light type where much weight cannot be allotted to the The chief point about the system is that there is no direct connection between the piston and the action, and the interposed spring ensures a slight delay in the unlocking of the bolt, producing a sweeter and less violent sequence of movements than could be achieved with a piston of the same weight directly operating the action. The Farquar-Hill Rifle is the only example of this system.
- by Recoil is the backward thrust or “kick” imparted to the weapon by the rapidly expanding gases produced in the chamber on combustion of the propellant. As the chamber is a cylinder, and the pressure set up is equal in all directions, its effect need only be considered in two of these: forward against the bullet; and backward against the base of the cartridge case. Forwards, resistance is offered by the inertia of the bullet and friction due to the setting up of the latter into the rifling; backwards, if the breech is securely locked to the chamber, the force exerted must overcome the inertia of the whole weapon; the cartridge case is thrust against the breech, the breech pulls upon the barrel, and the latt.er, unless free to move in a backward direction must carry the rest of the arm with it. As the pressure at any given moment, and therefore the force exerted, is equal in both directions, it follows that the bullet, offering a low total resistance, will have a high velocity imparted to it; while the opposite will be true of the breech and those parts of the arm to which it is secured, as the resistance offered here is a function of the relatively much greater weight of the whole weapon.
It will be seen that the force producing the phenomenon of recoil is exerted primarily upon the base of the cartridge case from the front (or inside), and is then transmitted to the breech, thence to the barrel, and finally to the whole arm, so long as each part is rigidly supported by the next in sequence of receipt. If, however, one part in the chain should not be secured, but is free to move in the direction of the force, then it is clear that a certain velocity will be imparted to it, and that it can be made to do work in consequence. Recoil-operation, then depends upon the principle that a part of the arm has imparted to it a relatively low velocity by the expanding gases of combustion, sufficient to do the work required in preparing the weapon for a fresh discharge.
It has been considered necessary to explain the phenomena of re coil at some length in view of the importance of this method of operation when considering Self-Loading Pistols, as all of them, with one or two unimportant exceptions, derive their power for operation from this source, though their methods of applying it differ considerably. .
Recoil systems can be classified according to the point at which the rearward thrust delivered by the expanding gas is translated into terms of movement of a part of the arm:
(1) Projection of the Fired Case.
(2) Projection of the Primer.
(3) Recoil of the Barrel.
(1) Projection of the Fired Case. This method of recoil operation is known generally as the “Blow-back” system. It depends entirely on the momentum imparted to the breech-block by the case as it is blown back out of the chamber, a movement which must be delayed until the bullet has cleared the barrel; otherwise there would be escape of gas at the breech which would damage the mechanism, lower the muzzle velocity and endanger the firer. This delay, or retarding effect to the backward movement of the breech action can be brought about in a number of ways, all of which will be fully discussed in the section on Self-Loading Mechanisms, but by far the commonest method in use with small caliber pistols taking standard ammunition of comparatively low power, is simply to have a heavy breech-block supported by a stiffish recoil spring.
The Blow-back system is perfectly satisfactory and reliable with small caliber cartridges of low power, for if the chamber pressure is kept down in the neighborhood of 2 tons, there is no need to make the breech-block unduly heavy or the recoil spring very strong. There is no doubt that a plain blow-back action (i.e., in which the breech is supported simply by inertia plus springs, unassisted by friction or other devices), could be built to take the most powerful cartridges, but it has been calculated that the American service cartridge, the M.1, developing a muzzle velocity of 2,600 f.s, would require a breech-block weighing 27 lbs., in such a case. As soon as chamber pressures exceed a value of about 2 ½ tons, a further difficulty occurs with blow-back actions. This is due to the fact that the cartridge case begins to move back immediately upon firing, so that the maximum chamber pressure is reached with the case partly unsupported and yet with the forward portion tightly gripped by the walls of the chamber.
Parallel-sided cases are desirable for blow-back actions to prevent the escape of gas round the outside of the moving case, but it is for this very reason that they are so tightly gripped by the walls of the chamber; burst and separated cases must occur unless the brass is specially thick at the danger point about ¼ in. from the base of the case, and this liability to “separations” increases greatly with higher chamber pressures. Powerful ammunition, however, is made use of with several guns which have plain or amplified blow-back actions, and this difficulty is got over in one or two different ways, either by reinforcing the case at the “danger point”,-an expensive method only justifiable for special weapons-or by lubrication of the case . The Becker .8 machine-gun is an example of the first method; It 1s a heavy anti-tank m.g. with a slow rate of fire and uses heavy brass cases specially reinforced at the base.
Lubrication not only prevents gripping of the case but it also acts as a gas seal, (it incidentally raises the chamber pressure), and enables a coned case to be used satisfactorily, thereby lessening all difficulties of extraction.
The best known example of this system is the Schwarzlose Machine-gun M.1912, which takes the 8 mm. Mannlicher cartridge (M.V. 2032 f.s.), and oils each case as it is fed into the chamber. The Thompson Self-Loading Rifle also provides for lubrication of its ammunition by special oil pads of fabric in the action. Both of these guns have blow-back actions in which the inertia of the breech is assisted by additional delaying devices.
The Pedersen, a recent self-loading rifle lately under test for the U.S. Army, which has a blow-back action with friction assistance, employs hard wax as a lubricant. This is not provided by the act on as in the Schwarzlose and Thompson, but by each cartridge, which is covered by a thin film of the wax before issue.
One of the chief reasons why the earlier designers of self-loading pistols favored some form of locked breech was this difficulty of separated cases which occurred with blow-back actions and high-powered ammunition. Bergmann, who made pistols with plain blow back actions some years before any other designer, succeeded in getting over the difficulty by sacrificing some of the efficiency of his ammunition. In one of his earliest models (1894) he used a powerful cartridge of 6.5 mm. (.256) caliber, developing a muzzle velocity of 750 f.s., but not only is the case quite steeply conical, in addition the chamber is provided with a large gas escape port on the right side. In other words, he deliberately allowed for consider able loss of gas round the outside of the moving case, but directed it away to the exterior where it could not damage the mechanism. That considerable loss of efficiency occurs in the normal way with this arrangement is shown if one fires an oiled round from one of these pistols; for the effective gas-seal round the case results in violence for which the action was obviously never designed. On the other hand, a separation could probably never occur even with a weak and thin case. It is interesting to note in this connection that Bergmann evidently thought it necessary to provide a similar gas escape in the case of his 1897 Military Model, which has a very interesting locked-breech mechanism with recoiling barrel, and which, theoretically at any rate, should require no such thing.
Another early blow-back pistol which used powerful ammunition, the Maxim, also made use of gas escape ports, but in this case there are two of them, one on each side of the chamber; probably in this instance one was not enough, as the cartridge (8 mm. Schonberger) is even more powerful than the 6.5 mm. Bergmann.
The blow-back system is by far the most widely used of any system for self-loading pistols, and especially for the smaller calibers, which embrace the vast majority of makes; the various types of mechanism employed on this principle will be described in the next section.
There is one further type or variation of simple blow-back action to be discussed before going further. It depends upon exactly the same principles as those already described, but might almost be termed a “blow-forward” action, because instead of the projected case thrusting the breech back against the resistance of a spring, the breech is rigidly fixed to the frame of the weapon, and the barrel is free to move forward against a spring. The case is gripped by the extractor, and upon discharge the expanding gas propels both bullet and barrel forwards, but just as in the more usual system, the inertia of the bullet is very many times less than that of the barrel and the resistance of the recoil spring, so that the bullet is driven out of the barrel by the gas pressure before the same force has had time to overcome the inertia of the moving parts, in this case the barrel itself and its recoil spring. Thus it will be seen that this forward-moving barrel system depends upon exactly the same principles as all other blow-back actions; the force of projection of the fired case is simply directed forwards instead of to the rear.
Examples of this system are rare; and are limited to pistols. In two instances the arms were made in some quantity; they were the first Mannlicher pistol of 1894, and the .32 caliber Schwarzlose of 1908. The Mannlicher was not very successful and is now rare, but the .32 Schwarzlose is still current and was quite popular, though it is now no longer made. In addition, one of Browning’s earlier patents described a pistol in which the barrel was made to move forward by a lever which was blown off a gas-port on the upper side of the barrel; this, of course, was in no sense a blow-back action, and is simply mentioned in connection with forward-moving barrel systems.
(2) Projection of the Primer. This method of recoil operation uses the force of projection of a part only of the fired case, namely the primer. The chief advantage to be gained by this is that the breech and cartridge case can be rigidly supported until the bullet has left the barrel, a state of affairs which is essential for the successful use of high-powered ammunition, in that is does away with the moving parts necessary with blow-back systems, and also the difficulties of extraction described in the last section on the latter. Such an action is described as a “locked-breech”; its essential condition is that the barrel and breech are positively locked together until the bullet has left the muzzle and the gas pressure has disappeared;, its most usual form employs a recoiling barrel.
In primer operated systems the barrel is fixed, and the cartridge is provided with a special type of primer which is sunk in the primer pocket rather more deeply than is the usual practice, so that it is capable of a considerable degree of movement in a backward direction. In another gun (Garand Primer Operated), a standard cartridge and primer are used, but the striker is cup-shaped and fits over the latter. Initially, the method of operation is the same in each case; upon discharge the cartridge case cannot move, but the primer, is forced back by the gas-pressure and impinges upon the striker. This has a certain velocity imparted to it and in moving back un locks the breech.
In the Roth system where a special deep primer pocket is used, the energy imparted to the heavy striker mechanism is sufficient not only to unlock the breech, but also to withdraw the breech-bolt against the resistance of the recoil spring; in other words, the arm is actuated entirely by the energy obtained from the primer. This system has been applied by Roth to a pistol and to a self-loading rifle. In the Schonberger pistol, which appeared some years before Roth’s patents were filed, the striker moves back 3/16 of an inch before the breech blocks; this must also suppose a special deep primer pocket, though It would appear that some energy might still remain from the gas within the case to assist forcing back the bolt, which with the striker is comparatively light. In the Garand system, which uses standard primers, the striker moves back only 3/i00ths of an inch to unlock the breech, so that when this occurs the bullet is still in the bore and there is sufficient gas-pressure in the barrel to throw the bolt to the rear and work the self-loading action. This is therefore not a true locked-breech system, but more of a delayed blow-back; it would probably work only with a long barrel for the same reason that applies with direct gas operation when the port is situated near the muzzle; namely, the pressure is comparatively low and gives a less violent impulse. The two instances are exactly comparable, for in the Garand the fired case is “released” when the bullet is nearing the muzzle; it is simply a case of a gas-port at the rear. The Garand rifle is well designed and operated with more than usual reliability in the U.S. Army tests. ·
(3) Recoil of the Barrel. There are numerous systems applied to both machine-guns and self-loaders which make use of recoiling barrels. The breech is always locked, and the energy· of recoil is converted into a backward movement of the barrel and breech together until the projectile has left the muzzle, when either the barrel movement is checked and the breech continues its travel to perform the operations of extraction, ejection, feed and recocking, or the barrel is returned while the breech mechanism remains momentarily in position before moving forward to do that work.
Thus recoiling barrel systems can be sub-divided into two groups:
- Short Recoil Systems
- Long Recoil Systems
- Short Recoil The terms short and long recoil are used in a relative sense; in self-loading or automatic weapons of the short recoil type the backward movement of the barrel is much less than the length of the cartridge, but varies considerably in different designs, so far as actual distance of movement is concerned. The principal effect of short recoil is that the breech must be allowed to continue its backward travel after unlocking, which must occur as the barrel stops, in order to perform the cycle of automatic operation. This presents no difficulties as regards self-loading arms, but in the case of fully automatic guns the rate of fire would be seriously reduced unless some means are introduced by which the speed and distance of travel of the lock are accelerated relatively to those of the barrel.
For self-loading pistols a short recoil system is by far the most usual, and is employed in all the most successful locked-breech actions. The distance of travel of the barrels of these various types are widely different; the shortest is the .455 Webley (1906) with 3 mm., one-eighth of the length of its cartridge; while the longest is the 8 mm. Roth-Steyr with 9 mm., or practically half.
Examples of short recoil systems are:
Mauser, Luger-Parabellum, Colt, 1897 Bergmann, Bergmann-Bayard, 1902 Mannlicher, Glissenti, 1911 Steyr.
Maxim types, Browning (heavy), Furrer.
The only examples of short recoil self-loading rifles are a few experimental weapons such as the Mannlicher.
- Long Recoil Systems. Long recoil is also a relative term; the expression implies that the barrel recoils locked to the breech until the latter has reached the end of its travel, and therefore for a greater distance than the length of the The barrel must also re turn appreciably before the bolt is released, to allow for extraction, ejection and feed to take place as the latter moves forward, or in other words, the breech is opened only on the return “stroke”; whereas in short recoil systems it is opened on the recoil stroke.\
The long recoil system is thus rather slower in operation than the short, but this is of no consequence with self-loaders; with automatics, however, it affects the rate of fire, making it even slower than. the short recoil designs, though the difficulty is generally got over by introducing the fresh cartridge before the barrel has reached the firing position.
Long recoil systems are rare in pistols and automatics; but are well known and familiar in shot-guns and in a widely known sporting rifle. Examples:
Mars, Frommer, Roth-Sauer. Rifles:
Remington, Mauser 1902.52
Browning, Winchester. Light Automatics:
- Operation by a Combination of Gas and
This method has been applied to several guns, notably of the Maxim type, with marked success, and also to one experimental pistol. Examples:
German Maxim. (Heavy and Light Models.) Chauchard.
These are all machine-guns.
The design is almost exactly similar in each of these machine-guns. A muzzle attachment is screwed to the water-jacket (or barrel casing in the case of the Chauchard) which traps some of the gas on its exit from the barrel in such a way that recoil of the latter is assisted. There is no piston or other reciprocating mechanism, the barrel may be said to be blown back by the muzzle-blast; in fact, these guns are recoil operated with some gas assistance. They will, of course, work with out the muzzle-attachment, but the latter undoubtedly increases the rate of fire and at the same time has a further important military ad vantage in that it hides the flash to a large extent.
It will be seen from the foregoing analysis of the principles of automatic operation that as far as self-loading pistols are concerned, the use of recoil as a means of providing the energy necessary to work the arm overshadows all other systems both in numbers and importance. Indeed it can be said that recoil operation is the only method in serious use, though there is considerable variations: the mechanical application of it embodied in a large number of designs. In general it may be said that the earlier self-loading pistol, and all those weapons that use powerful or fairly powerful ammunition, including self-loading rifles, have some form of locked-breech action which makes use of a recoiling barrel; while nearly all the small caliber pocket weapons depend upon the “blow-back”, or unsupported breech system, which has been shown by experience to be quite adequate for the smaller and weaker cartridges in general use
with these pistols.
AUTOMATIC AND SELF-LOADING MECHANISMS
Having considered at some length the principles of which automatic fire is to be obtained, it is now necessary to classify the various mechanical systems which have been evolved for recoil operation. These can be divided into three main groups:
- Locked-Breech Recoiling Barrels.
- Unassisted Blow-Back Systems. Resistance to the gas pressure depends only upon the inertia of a comparatively heavy breech-block plus springs.
- Amplified Blow-Back Where the simple inertial factors are assisted by friction or other devices. Known also as “delay” actions.
- Locked-Breech Systems. With the exception of the rare primer-operated guns, the principle of which was described in the last section, and one other system, the Hammond, all recoil-operated locked-breech systems depend upon a recoiling barrel. As the mechanical methods only of locking the breech are to be considered, the classification into short and long recoil systems is of no advantage here; examples of both systems will be placed in the categories under which they belong according to their methods of breech locking. Actions will be assumed to be on the short recoil system unless other wise specifically described as long recoil.
The following methods of locking the breech are found:-
- Moving Wedges. Rocking or rising and falling wedge-shaped members fit into recesses in the bolt and are disengaged on recoil of the barrel.
Mauser (Rocking lugs)
Mannlicher 1902 (Horizontal rocking plate) Reifgraber (Rocking bolt)
Charola-Anitua (Vertical rocking arm and stud) Glissenti (Vertical swinging block)
Bergmann-Bayard (Falling block through which bolt passes) Webley 1904 (Rising wedge)
Revelli (Vertical swinging block) Rifle:
Mannlicher 1904 (Horizontal rocking plate) Shot-gun:
Browning (Lug and slot on barrel extension; long recoil)
- Toggle-Joint. The principle of a toggle-joint is somewhat like that of the human knee-joint in walking. The breech-bolt is jointed with the rear arm pivoted to the barrel extension, so that when the breech is closed the two arms which comprise the “toggle” are in one straight line in prolongation of the bolt, and cannot move until their common pivot is thrown off dead center. Upon discharge the force of recoil is taken by the bolt and transmitted through the arms and their pivot pins to the barrel extension, the bolt is quite immovable and recoils with the barrel until the joint is “broken” by forcing its pivot off dead center, after which the bolt continues its travel alone, extracting and ejecting the fired case. The toggle-joint system provides one of the strongest and most rigidly locked forms of breech mechanism in existence, as the chamber cannot possibly be opened until the joint is “broken”; a good deal of strain is, however, placed upon the pins which articulate the arms, as they transmit the whole force of the recoil to the barrel. It is an action which requires first class material and faultless machining to work reliably, and is therefore expensive to produce.
Borchardt (Rising joint)
Luger-Parabellum (Rising joint)
Ross (Rising joint, with links in pairs; those pivoted to the barrel folded outside and lying parallel to the inner, or breech links in the closed position)
Maxim: and all Maxim types. (Inverted, or falling joint) Vickers, Parabellum, etc.
Furrer (Rising joint) Rifle:
Walther (Inverted joint)
- Displacement of Barrel or Breech-Block. Barrel and breech block are in alignment at the moment of firing and recoil locked together; unlocking is accomplished by the displacement of one or other either vertically or laterally.
Colt-Browning (Vertically; by parallel links)
Colt (Model of 1911) (Vertically; by single link at rear; barrel sup- ported at front)
Webley (Vertically; by sliding inclined tongues and grooves)
- Displacement of the Breech-
Bergmann 1897 (Laterally; by lugs on receiver frame)
Knoble (Vertically; breech-block raised out of engagement with locking lugs by rocking links)
- Rotatory Systems. These methods of breech locking all de pend upon some degree of rotation being imparted barrel or breech-bolt. With regard to turning barrel systems, it .has been claimed in several instances that this rotation is in some degree imparted by the bullet engaging in the rifling, and in others that the spinning bullet prevents unlocking of the breech where this depends upon rotation of the barrel against the twist of the rifling. It is a little difficult to believe this when the greatly disproportionate inertia of a bullet is compared with that of even the lightest of barrels; in fact, it can be said quite definitely that in every case where rotation is imparted to a recoiling barrel it is effected by inclined lugs engaging in grooves cut on a steep pitch, a “quick thread” principle; or, in other words, that the recoiling breech-block pulls on and twists the barrel as it moves back.
(a) Rotation of Barrel. The systems which come under this heading differ very considerably in what might be called the degree of breech-locking obtained. At least one of them, the 1911 Steyr, has as positive a lock as for instance the Mauser; in others the locking pro vided for is of the slightest, and cannot produce more than a very short delay in breech opening; actually these depend for their success upon the same factors as many blow-back actions, viz., a fairly heavy breech-block and recoil spring with the addition of some frictional elements. Turning barrel systems have for this reason been variously described by some authors as “semi-locked actions”, and as “hesitation” or “delay systems”; but strictly speaking they should be classified as locked-breech mechanisms because in every case the breech is undoubtedly locked to the barrel at the moment of firing, though it is pretty certain that in one system, the Savage, opening of the breech starts to take place almost immediately, probably as soon as with any blow-back action, but this is of no great moment as the ammunition used is of low power. There is, however, some justification for the claim, (in the case of the Savage) that the breech-block and recoiling parts can be made lighter than they would need to be if the action were a plain blow-back one; in actual fact the Savage breech is lighter than that of any blow-back pistol firing the same cartridge; but it should also be stated that the Savage has in the opinion of many a noticeably unpleasant recoil, which is probably not unconnected with this reduction in weight of the recoiling parts.
Schwarzlose 1895 (Long recoil)
Browning 1897 ( 2)
Roth-Steyr (90 degrees of rotation)
Steyr 1911 ( 60 degrees of rotation)
Savage (5 degrees of rotation)
Czech 9 mm. 1925 (30 degrees of rotation)
These are all pistols; so far as is known no rifles or machine-guns have been designed on a turning barrel system. The Savage also differs from all the other turning barrel systems in its extent of barrel recoil, for this is very short and indeed is practically negligible, the barrel lug being given just sufficient play in its seating on the receiver to allow of the turning movement imparted by an obliquely cut shoulder on the breech slide. The· 1897 Browning, Roth-Steyr and Steyr-Hahn allow considerable recoil of the barrel before unlocking occurs, (half an inch in the case of the second pistol) while the 1895 Schwarzlose is a long recoil system.
(b) Rotation of Breech-Bolt. Systems on this principle are relatively more frequent than turning barrel actions. They all provide locks of the most positive order, and the principle lends itself particularly to long recoil mechanisms.
Schwarzlose 1898 (Short recoil)
Hauf (Short recoil)
Clausius (Short recoil)
Mars (Long recoil)
Roth-Sauer (Long recoil)
All of these employ rotation of a solid bolt to lock the breech, with lugs cut on the bolt-head engaging in slots in the action-body or barrel extension, a principle similar to that in use with modern bolt action rifles. The Mars and 1898 Schwarzlose employ four segmental lugs and require a turn of one eighth of a circle (45 degrees) to engage in their recesses; the Hauf has three; while the Roth-Sauer employs but one only which engages in a recess above the entrance to the chamber and takes only about 20 degrees of rotation to lock the bolt. This unsymmetrical arrangement is theoretically objectionable because it gives rise to considerable vibrations in a vertical plane and is obviously a weak arrangement, but while such considerations are of great importance in a rifle, affecting both strength and accuracy, they are really quite negligible in a pocket pistol firing a comparatively weak cartridge such as this. The Krag-Jorgensen Rifle is the classical example of a single bolt lug in which asymmetrical stresses are produced. Clausius has a single large stud or pin engaging in a slot at the side of the barrel extension in his original specification, but adopted four segmental lugs in a later model. One of his patents introduced a further novel feature; the barrel is fixed, but the chamber, which consist of a steel liner within the barrel, recoils locked to the bolt and behaves in other respects as a moving barrel. The Mars and the 1898 Schwarzlose are adapted to powerful ammunition and require the strength of breech provided by their four lugs, and the same is probably true of the Hauf and the Clausius pistols, but the Roth-Sauer uses a short and relatively weak 7.65 mm. cartridge.
There is a further class of turning-bolt action applied to pistols in which the bolt-head alone rotates. The head, which carries the locking lugs, has a tail which fits into the bolt cylinder and is pro vided with two helical grooves which engage with feathers on the inside of the cylinder. The bolt-cylinder cannot revolve owing to its ribs working in grooves provided in the breech slide. The bolt-head, on the other hand, cannot move backward until the locking lugs have been disengaged from their recesses behind the chamber, and this can only be effected by the rotation given to the tail of the bolt-head by the feathers on the inside of the bolt cylinder working in the helical grooves. The action is in effect a “straight pull” bolt action exactly analogous to such Straight-Pull Rifles as the 1895 Mannlicher, the Ross and the Schmidt-Rubin; and it will be realized that such a system is only possible of application to a self-loading arm using the long recoil principle, for the reason that the force required to open the breech must be applied to the bolt-cylinder and nowhere else; no amount of pressure on the face of the bolt-head can possibly disengage the locking lugs from their recesses. The sequence of operations then is as follows: the barrel and bolt recoil locked together for the full extent of the recoil stroke, loading up (i) the barrel recoil spring, and (ii) the bolt recoil spring. At the end of recoil the bolt cylinder is caught by a suitable catch, but the barrel is returned by (i), thus applying the force at the only point which will unlock the bolt-head. Extraction and ejection now take place on the return stroke of the barrel, the final movement of which trips the bolt cylinder retaining catch; as the bolt returns it feeds a fresh round from the magazine and locks home the bolt-head.
There are three pistols on the “straight-pull” system: Woodgate
The Woodgate employs two lugs on the bolt-head, symmetrically disposed at I So degrees and horizontal in the locked position; the 1901 Frommer has two at 90 degrees with the extractor between them, and the 1912 Frommer one only.
Both of these arms employ two symmetrically disposed lugs which are vertical when locked. The Mauser was intended for full powered military cartridges, but the Remington models are all sporting weapons for ammunition of medium power.
There is one other pistol which has a turning bolt action on the short recoil system which is unique in that rotation of the barrel is used as well. This is the Hellfritzsch, The bolt has no separate head, but is locked to the barrel by helical projections engaging in similar grooves. Barrel and bolt recoil together, rotation being imparted to the barrel by a stud running in a helical groove on the latter. The bolt follows the barrel because of the locking projections; i.e., it tends to be screwed up to the barrel. After a short distance a groove on the bolt engaging with a stud on the receiver becomes helical and the bolt consequently rotates further, unscrewing itself from the barrel and opening the breech. It is an ingenious action but has no particular advantages.
Machine-Guns which have turning-bolt actions: Lewis
Hotchkiss (.303 British model)
These are, of course, both gas-operated guns, but their system of breech locking depends upon a turning bolt action. The French 1917 Self-Loading Rifle is also a gas-operated arm on the same principle; i.e., a “straight-pull” bolt action worked by a gas piston.
Chauchard (Long recoil)
Frommer (Long recoil)
- Simple or Unassisted Blow-Back
The vast majority of small caliber pocket pistols are designed on this system. There are also a certain number which use a medium powered cartridge successfully with it. Examples of the simple blow back system are very numerous: the largest caliber (in commercial, as distinct from experimental) pistols is 9 mm., with about moo f.s. muzzle-velocity. The only fully automatic weapons on this system are the Bergmann Musquete and the Becker .8 in. Machine-Gun.
- Amplified Blow-Back or Delay Systems.
The inertia of a heavy breech-block and recoil-spring is assisted by:
- Devices giving additional frictional resistance to the movement of the breech-
Bergmann 1901 (Wedge opening head of breech-bolt against sides of action-body)
White-Merril (Friction against inclined surfaces: breech-block forced upward by cam)
Mannlicher 1901 (Cam held in contact with breech slide by mainspring)
These are all pistols firing comparatively high velocity cartridges. Friction delay actions have been applied particularly to low velocity automatic guns which use pistol ammunition of the higher powered order, and also extensively to self-loading rifles and carbines. A breech system of this type is very suitable for these weapons, as they can be made rather heavier than pistols and their ammunition is not so powerful as to render a locked breech imperative.
Thompson Sub-Machine-Gun (Friction against inclined sur faces: H-block)
Villar-Perosa (Friction of turning-bolt)
Both of these automatics, and the Bergmann Musquete also, rely principally on inertia for their working, as they all three possess breech-blocks which are very heavy in comparison with bullet weight, very much more so than any self-loading pistol. The factors which are involved in their system of operation may be summarized as follows: ·
- Inertia: Very heavy reciprocating
- Friction: This element is most pronounced in the Thompson, rather less so in the Villar-Perosa, and absent in the Bergmann.
- Momentum acquired by the heavy breech-bolt on its forward travel: The cartridge is actually fired just before the breech is home, so that the explosion gas acting upon the fired case has first .to stop the forward movement of the breech block or bolt and then to force it
With Self-Loading Rifles designed to use a full powered military cartridge the problem is not capable of so simple a solution. Re coiling barrels are not desirable in arms of this type, and as it has al ready been pointed out, considerations of weight preclude the use of a plain blow-back action; some sort of delay action therefore constitutes the ideal, but the frictional or other supplementary element must be pronounced and efficient.
Examples of rifles taking full powered ammunition:
Marga . (Piston and springs inclined at an angle to axis of recoil)
Warnant-Creon (Multiple rocking cams; having the effect of “gearing” with considerable friction)
These are both early experimental rifles; the patent records of the first decade of the 20th century are full of similar attempts to produce arms of this nature.
Lubrication of the cartridge has always been a difficulty, but, lately in America, delayed blow-back systems for rifles have met with more success, viz.,
Thompson Semi-Automatic Rifle (Quick-threaded screw breech bolt opening slowly under gas pressure)
Pedersen Rifle (Toggle-joint with cam surfaces)
The inventor of the two Thompson arms has always claimed that an entirely new principle of breech action is employed in both the sub-machine-gun and the rifle, though it is applied rather differently in each case. It is known in America as the Blish Principle, and is said to depend upon the adhesion of plane surfaces under pressure. In the case of the Thompson arms the theory is as follows: Immediately after the discharge the pressure on the head of the breech bolt is very high, and the inclined plane surfaces of the “lock”, (H-block in the sub-machine-gun, and quick-thread turning bolt in the case of the rifle), adhere firmly and prevent immediate opening of the breech; as the bullet leaves the barrel and the chamber pressure falls, adhesion of the inclined surfaces becomes less, slipping between them occurs and the breech opens.
It is, however, very doubtful if the so-called Blish principle exists; most of the available evidence goes to show that if two surfaces will slide under one pressure they will do so equally well under a heavier pressure, arid in practice the sub-machine-gun works quite well with the H-block with its slipping surfaces removed. This fact goes to show that in any case the pure frictional element, quite ap rt from any adhesion under pressure, is of very little importance in the efficient working of the gun; the true secret of its success lies in the use of the energy provided by a very heavy breech-block on its forward travel. In the case of the Thompson Rifle the frictional element is undoubtedly of much greater importance, as the cartridge is of much greater power and the breech-bolt is very much lighter, but it would appear to be 11imply a case of finding the correct pitch for the screw breech which will apply sufficient friction to suit the chamber pressure of the cartridge.
Deutschmann, Millier and Stroh (liquid buffer).
This ingenious specification, applied to a pistol, directly follows the principles employed in the buffer gear of Q.F. ordnance. The rear end of the breech-bolt forms a piston which on recoil forces liquid through small channels to compress the recoil spring while on the “return” or “run-up” stroke the fluid is by-passed into the piston chamber by a suitable valve.
(ii) Momentum Block Systems. The essential principle of breech systems of this type is that the reciprocating mass of the breech is in two parts; (1) the “head”, which supports the cartridge, contains the striker and is comparatively light; and ( 2) the “block” which is considerably heavier than the “head”, and which can only receive the force of recoil indirectly, through the latter.
The barrel is fixed; and upon discharge the two parts of the breech recoil together for a very short distance (2 mm. in the Remington). At this point the “head” is locked to the action-body, while the heavier “momentum-block” continues its travel and after a certain distance (7 mm. ibid) unlocks the “head” and carries it back to complete the opening of the breech.
Remington 5 1 (Pistol)
Rheinische M-und-M 1910 (Rifle)
Freeman 1904 (Carbine: pistol ammunition)
Sjorgren (Shot-gun) .
It has been claimed that the Momentum Block System provides a locked breech at least as positive as that in many moving barrel actions such as the Glissenti and Revelli actions for instance; but there no doubt that the breech must start to open immediately upon discharge, and that primary extraction and consequently some, gas escape takes place before the “head” is locked and possibly before the bullet has left the barrel. The Momentum Block is undoubtedly a delayed blow-back system.
(iii) Inertia Assisted by Leverage. In actions of this type the breech-block does not compress the recoil spring directly as in all the types so far considered, but it does this indirectly through the medium of levers, usually in the form of an elbow joint . The result is that resistance to the movement of the breech is increased by friction to a very slight degree, but chiefly because levers are of the third order and work at a disadvantage in loading the recoil spring.
Andrea Schwarzlose was the great protagonist of this type of action; it has only survived in machine-gun form, the pistols were abortive.
Finally there is another form of blow-back action which has already been discussed to some extent, that in which the barrel moves forward while the breech remains fixed.
These are all pistols. The Komuro action is ingenious but of doubt value. According to the specification, the barrel is held in the forward position, with a cartridge in the chamber, by a spring catch. Pressure on the trigger releases this catch and allows the barrel to fly back, against the standing breech, the cartridge being fired by its impact on the point of the firing pin which’ projects from the face of the breech. Upon discharge the barrel is blown forward and retained thus, while a special feeder carries a fresh cartridge to the chamber. Comment is needless.
This finishes the outline of the principles of automatic action and also of the varied mechanical means by which they are applied to selfloading arms and to machine-guns. As far as pistols are concerned, actions will be dealt with in greater detail when the arms themselves are described, and at the same time such points as trigger mechanisms and magazine systems peculiar to self-loading weapons will be discussed.
Machine Guns have been cited in this outline as examples of particular types of automatic systems rather in comparison with selfloading types; it is not intended in this volume to go further into the details of full-sized guns of this nature. The information in this section comes from Textbook of Automatic Pistols by R.K. Wilson.