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and extracts the case. While the wedge is being withdrawn the firing pin is pulled back and cocked for the next round. The mechanism is closed by reversing the hand lever; this rotates the breech block upwards and pushes home the cartridge case, and the wedge is then forced up and secures the breech block.

These small type Q.F. guns, which were introduced to cope with torpedo boats, are now, however, of little account, since experiment has proved that nothing smaller than a 12-pounder is sufficient so to injure a modern torpedo boat as to stop it. Most of these small guns are therefore in the English and in some other Services being converted into "sub-calibre guns for exercise purposes. These sub-calibre guns retain their ordinary breech mechanism, but the bodies are fitted with a strong steel plug screwed on the outside in a similar manner to the breech screw of the parent gun. The sub-calibre gun is placed in the parent gun and the screwed plug engages in the threads of the breech opening. There has been a gradual development of ideas regarding the repelling power required by a vessel against torpedo boat attack. The 12-pounder Q.F. 40-calibre guns were replaced by the more powerful 12-nounder Q.F. 50-calibre gun; this again by the 4-in. high power gun of 50 calibres, and now 6-in. guns are being used.

One other form of sliding mechanism is of importance owing to its adoption for the 75 m/m. French long recoil field gun (see below: Field equipments). This mechanism is on the Nordenfelt eccentric screw system and is very similar to that proposed by Clay about 1860; it has a breech screw (fig. 36) of large diameter mounted in the breech opening, which is eccentric to the bore. For loading, the breech block has a longitudinal opening cut through it, so that when the mechanism is in the open position this opening coincides with the chamber, while a half turn of the breech screw brings its solid part opposite the chamber and closes the gun. The mechanism is very simple and strong, but it is only suitable for small Q.F. guns using cartridge cases; the firing gear is similar to that applied to other types of mechanism, and the fired case is extracted by an extractor actuated by the face of the breech screw as it is opened.

With the swinging type of breech mechanism we are confronted with numberless patterns, many of undoubted merit and claiming certain advantages over others, and all showing the vast amount of ingenuity expended in so designing them that they may be as simple, and, at the same time, as effective and quick

acting as possible. It is impossible to deal with all these, and thereLore only the more important systems will be described. The special feature of this type is that the breech is closed by an interrupted breech screw; the screw is either supported in a carrier ring or tray hinged near the breech opening, or on a carrier arm which is hinged near the outer circumference of the gun.

The screw may be of the cylindric interrupted, Welin and coned types; these, or their modifications, practically embrace the various forms used. The cylindric form (fig. 37) is the simplest; it consists of a strong screwed plug engaging with a corresponding screw

thread cut on the interior of the breech opening of the gun. The screw surface of the breech plug is cut away in sections equally divided and alternating with the threaded portions. The screw surface of the breech opening is similarly cut away, so that the plug can be pushed nearly home into the breech opening without trouble; by then revolving the breech screw through a small angle the screwed portions of the plug and breech opening engage. Thus if three screwed sections alternate with three plain sections the angle of revolution necessary to ensure a full engagement of the screw surfaces will be 60°. The Welin screw (fig. 38) is an ingenious adaptation of the cylindric type; in this the surface is divided into sections each formed of two or three cylindrical screwed steps with a single plain portion; thus if there are three sections, each section of which has one plain division and two screwed divisions, there will be in all six screwed portions and three plain. The breech opening is correspondingly formed so that the screwed threads would fully engage with 40 of movement. There is consequently a greater amount of screwed circumferential surface with the Welin screw than with the ordinary cylindric interrupted type; the latter form has 50% screw surface while the Welin has 60%. For equal screw surface the Welin can therefore be made shorter.

For medium guns the Elswick type of coned screw (fig. 39) has found much favour, and this mechanism has been fitted to guns of all calibres from 3-inch to 6-inch, both for the British and numerous other governments. The coned breech screw is formed with the front part conical and the rear cylindrical, to facilitate its entrance into the gun, and also its exit; this form, moreover, is taken advantage of by cutting the interruptions in the screwed surface alternately on the coned part and on the cylindrical part, so that there is a screwed surface all round the circumference of the breech screw. By this means the stress is taken all round the circumference, both of the breech screw and in the gun, instead of in portions alternately, as with other forms.

The Bofors breech screw is a modification. The surface is formed of a truncated ogive instead of a cylinder and cone, and the threaded portions are not alternate.

In the older types of mechanism for heavy B.L. guns the breech was opened in from three to four different operations which involved considerable loss of time. Fig. 40 shows the general type for 9-2-in., 10-in. and 12-in. B.L. guns. To open the breech the cam lever C was folded up so that it engaged the pin B in connexion with the

FIG. 33.-Krupp Breech Action.

ratchet lever E. This was worked and so disengaged the breech screw from the threads cut in the gun; the cam lever was then folded down as to to start the breech screw, and the winch handle Q rotated and so withdrew the screw and swung it clear of the breech opening. During these operations the firing lock was actuated and made safe, but the fired tube had to be extracted by hand. To close the gun these various operations must be reversed, and to open or close the gun would certainly occupy at least half a minute with trained men.

To compare with this a modern 12-in. breech mechanism is shown in fig. 41. In order to open this breech it is only necessary to turn

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C

FIG. 35.-Nordenfeldt Q.F. Breech Mechanism.

that the cam acting on the rear face of the gun releases the de Bange obturator, and the screw is then pulled by hand through the carrier ring out of the breech; (c) the carrier ring and breech screw are revolved together to the right, clear of the breech opening.

In a modern 6-in. gun fitted with de Bange obturator all these operations are combined and the mechanism (fig. 43) worked by a horizontal hand lever which is moved from left to right through an angle of about 200°. The hand lever A moves a link B connected to a pin C on the breech screw D and disengages the screw from the gun; a small lateral movement is then given to the axis pin of the carrier so as to allow the obturator pad E to swing out of its seating; when

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FIG. 34.-Hotchkiss Q.F. Breech Mechanism.

tooth B is moved from its extreme left position to the right, and so disengages the breech screw A from the threads in the gun; the rack A on the breech screw then comes into gear with the pinion E and draws the breech screw out of the gun into the carrier ring C, which finally swings on the axis pin and clears the breech opening. While the opening is being performed the firing lock is operated by the cam groove A; this puts the firing mechanism, either electric or percussion, to safety by withdrawing the firing needle, extracts the fired tube and leaves the primer chamber open for a fresh primer. All these operations are performed in the reverse order on closing.

With both these types of mechanism the de Bange system of obturation, with the pad only slightly coned, is used.

With smaller guns the mechanism is simpler, as less power is

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FIG. 36.-Eccentric Screw, Breech Mechanism.

this is quite free, the whole mechanism revolves on the axis pin and thus clears the breech opening. The firing lock F is actuated at the same time and ejects the fired tube G. A new tube is inserted while the gun is being loaded, so that immediately the breech is closed the charge can be fired without loss of time. In the old mechanisms the breech had to be closed first, and the firing tube inserted after.

The breech mechanism for Q.F. guns firing metallic cartridge cases is worked on similar principles, but is somewhat simpler than that for the de Bange obturation, due principally to the fact of the firing primer being already contained in the cartridge case when this is introduced into the gun.

In the English service the later patterns of breech mechanism for medium and heavy B.L. guns have a Welin screw, with a steep

All the recent patterns of mechanism have an extractor fitted to extract the empty cartridge case with Q.F. guns or the fired tube with B.L. guns. In Q.F. field guns it generally takes the form of a lever working on an axis pin. The longer arm of the lever is formed into a jaw which rests on the inner face of the breech opening beneath the rim of the cartridge case, and the short arm is so arranged that when the breech is opened the carrier, in swinging mechanisms, or the breech block itself, in sliding systems, suddenly comes in contact with it; the long arm is thus jerked backwards and extracts the case. In B.L. mechanisms the tube extractor is

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FIG. 37.-Interrupted Breech Screw-Cylindrical. cone de Bange obturator, supported on a carrier arm. This arrangement allows the mechanism (fig. 44) to swing clear of the breech opening immediately the threads of the breech screw are disengaged from those in the breech in a similar manner to the Q.F. guns fitted with a cone screw. The mechanism is actuated by the handwheel L which rotates the hinge pin; this in turn, through gearing, moves a crank arın D connected, by a link B, to the pin on the breech screw. By continuously moving the handwheel the link B is drawn towards the hinge pin until the breech screw threads are disengaged; the catch C then drops into a pocket on the breech screw and fixes it to the carrier arm. The whole of the mechanism then rotates around the hinge pin and leaves the breech open ready for loading. As the breech screw threads are being disengaged the electric or percussion lock W is operated by a cam groove in a similar manner to that already described. In the latest modification of this mechanism a roller at the end of the crank arm D works a long lever connected to the breech screw by two pins. This forms what is termed a "pure-couple" mechanism and it is claimed that greater ease of working is ensured by its use. While the loading is going on a new firing tube is

placed in the vent, so that on closing the gun, by turning the handwheel in the opposite direction, the gun is ready for firing. For 9-2-in. guns and those of smaller calibre the handwheel is replaced by a hand lever pivoted on the carrier (fig. 45). By giving this lever a single motion from left to right the mechanism is opened.

For 6-in. and 4-in. guns a shot support is attached to the breech face which is operated by the breech mechanism SO that when the breech is open the shot

support is in position for loading, and it falls out of the way when the breech is being closed.

In the larger types of all breech mechanisms ball bearings are employed in various parts, such as the hinge pin bearings, &c., to reduce friction and in most of the modern heavy guns on board ship the breech mechanism is arranged to be worked by a hydraulic cylinder placed on the breech face, or by a small hydraulic engine or electric motor placed in some convenient position on the mounting. The hand gear, however, is always retained for emergency and a dutch is provided so that it can be put into action at a moment's notice.

The Welin screw is largely used in the United States, but in heavy guns the ordinary cone (not "steep cone") de Bange obturator is employed. The screw is mounted either in a carrier ring or on a carrier tray. In France the ordinary type of interrupted screw is adopted and this rests in a carrier tray. The operations of opening and closing are very similar to those already described.

FIG. 38.-Welin Breech Screw.

arranged on the same principle but in this case usually forms part of the box slide, i.e. that portion of the mechanism attached by interrupted collars to the rear end of the vent axial, in which the firing lock slides as it is actuated by the opening or closing of the breech mechanism. When the breech is being opened the firing pin of the lock is drawn back to safety and the lock is moved aside from over the tube; a tripper then actuates the extractor and ejects the fired tube. The extractor and tripper are so contrived that when a new tube is pushed home the extractor is also pushed back into the closed position, or, if the tube is somewhat stiff to insert, the action of closing the mechanism moves the lock over the primer and forces it home. The firing lock used in B.L. guns is an important part of the

FIG. 39.-Elswick Coned Screw.

mechanism. They are all designed on the same principle, with a view to safety and rapidity, and may be regarded as a miniature sliding breech mechanism. In the older types the lock or its substitute was manipulated by hand, and with electric firing the wires from the tubes were joined up to the loose ends of the firing circuit;

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striker rides up an incline I (fig. 45) on the box slide and thus
pushes back the striker from contact with the tube.
tractor described above is actuated at the same time. Most locks
band To A

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FIG. 40.-Breech Mechanisms, Heavy Guns. consist of a steel frame with a socket for containing the striker and main spring. They are contrived so as to be capable of firing both electric and percussion tubes, but others are arranged for firing only electric, separate locks being employed for use with percussion tubes. The construction of both is very similar, but with the percussion lock, or the combined lock, a trigger is provided

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FIG. 42. Breech Mechanism, 6-in. B.L. Mark IV. which drops into a notch in the striker when this is pulled back by the lugs EE (fig. 45) on the outer attachment of the striker. On the trigger being pulled by a lanyard the striker is released and fires the tube.

For Q.F. guns with interrupted or coned breech screws the striker is contained in the breech screw, but, in order to provide for safety, a small lever cam or other contrivance is fitted which, when the mechanism commences to open, is operated by the hand lever and withdraws the striker from contact with the primer inserted in the cartridge

case.

The striker consists of a steel needle, with the stem insulated by ebonite or some similar material, contained The sheath is formed with in an outer steel sheath. a foot or lug which is acted upon by the safety gear; a collar is also provided for taking the thrust of the main spring.

Another form of lock now much in favour, especially for field-gun mechanisms, is that known as a trip lock. It is mainly used for percussion firing but can also be combined for use with electric tubes. In this pattern the striker is withdrawn, cocked and released by the continuous pull of a hand lever attached to the mounting or by a lanyard attached to the lock. Should a miss-fire occur the striker may be actuated as often as necessary by releasing the hand lever or lanyard and again giving a continuous pull (fig. 46).

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fit a special apparatus on the gun, so that directly the breech is
curious singing noise is heard at the same time. It is now usual to
rear end of the chamber and thus sweep the whole of the
partly opened a blast of compressed air is allowed to enter the
residual gas out at the muzzle.

Obturators.

The purpose of the obturator is to render the breech
end of the gun gas-tight, and to prevent any escape of
gas past the breech mechanism. In the first
Armstrong B.L. gun this object was attained
by fitting to the breech block a copper ring coned on
the exterior; the coned surface was forcibly pressed by
screwing up the breech screw against a corresponding
copper ring fitted at the breech opening of the gun
chamber. It is only possible to use this method when
the copper surfaces can be jammed together by a power-
ful screw.

Except the above, all obturators in use are arranged
to act automatically, i.e. the pressure set up in the
gun when it is fired expands the arrangement and scals
the opening; immediately the projectile leaves the bore
the pressure is relieved and the obturator, by its elasticity,
regains its original shape, so that the breech mechan-
In the French
ism can be opened or closed with case.
naval service B.L. guns have been in use since 1864, and
the system of obturation was arranged on the same expansion
principle as the leather packing ring of the hydraulic press. A steel
thick steel plate, carried on the face of the breech screw, so that it
ring A (fig. 47) of cupped form was fastened by a screwed plug to a
could rotate when the breech screw was rotated in opening or clos-
seating formed in the breech end of the gun chamber. When the
ing the gun. The outer lip of the cup fitted against a slightly coned
gun was fired, the gas pressure expanded the cup ring and forced
it into close bearing against the seating in the gun and the thick
steel plate on the breech screw, thus preventing any escape of gas.
Very similar to this was the Elswick cup obturator (fig. 48) intro-
duced by the Elswick Ordnance Company in 1881; its rear surface
was flat and it was held by a central bolt against the front of the
breech screw which was slightly rounded. The cup yielded to the
gas pressure until it was supported by the breech screw; this
action expanded the lip against a copper seating, let into the gun,
which could be renewed when necessary. Many of both types
are still in use and act perfectly efficiently if carefully treated.
The use of modern smokeless powder renders them and similar
devices, such as the Broadwell ring (fig. 49), &c., peculiarly liable to
damage, as a slight abrasion of the lip of the cup or ring, or of its
Unless, therefore, the fault be immediately
each round fired.
seating, allows gas to escape, and so accentuates the defect with
remedied considerable damage may be caused to the gun. The
Broadwell gas ring is still in use in the French naval service, where

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In all modern heavy guns, especially when firing to windward, there is a tendency, when the breech is opened rapidly after firing, for a sheet of flame to issue from the open breech. It was practically unflash. known with the old black powders, but is of frequent occurrence with all smokeless propellants. If the gun is loaded immediately after the breech is opened the fresh charge may be ignited and an accident caused. Several serious accidents have already been traced to this on the United States battleship cause, notably one "Missouri" on 13th April 1904, when 33 lives were lost. The flame is due to the large amount of highly heated carbonic oxide remaining in the gun from the explosion of the charge; this mixing with the oxygen of the air when the breech is opened burns rapidly as a sheet of flame in rear of the gun, and should wind be blowing down the gun the | action is more intense. By looking into the gun from the muzzle, before the breech is opened, the gas can often be seen burning with a pale-blue flame as it slowly mixes with air and a

FIG. 43.-Breech Mechanism, Modern 6-in. Gun.

it is made of copper (fig. 50), and also of steel in a modified form
In the French navy, as in
(Piorkowski) in the German service (fig. 51); in the last-named service,
and heavy, use metal cartridge cases.
owing to the defect already named, all the latest guns, both light

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