GENERAL DESCRIPTION.
Weight of the ·303-in. gun, 60 lbs. Weight of the tripod, 48 lbs. Weight of ammunition box containing one filled belt, Mark VI 21 lbs., Mark VII 19½ lbs.
The gun may be considered as divided into two portions—the non-recoiling and the recoiling. It is worked automatically by two forces—the explosion of the charge which forces the recoiling portion backwards, and a strong spring (called the fusee spring) which carries it forward.
Non-Recoiling Portion.
The non-recoiling portion consists of the barrel casing and breech casing, and is attached to the mounting by the crosshead and elevating joint pins.
The barrel casing is of gunmetal, holding about seven pints of water to keep the barrel cool when firing; it has three openings, one on the upper right side near the breech for filling, one underneath near the muzzle for drawing off the water, and the third (also near the muzzle) for allowing the steam, but not the water, to escape. The first two are closed with screwed plugs; the last is open and connected with the steam tube, and carries the condenser nipple.
A cork plug is provided which can be inserted in the steam escape hole when the gun is travelling, in order to prevent waste of water from jolting. The plug should always be taken out before commencing to fire, and put in again before the gun changes position, unless the condenser is attached to the barrel casing and can be conveniently moved with the gun.
To prevent the escape of water, there is at the forward end of the barrel casing asbestos packing, which is held in position round the barrel by the packing gland. At the rear end of the barrel there is a cannelure, also filled with asbestos packing, which prevents the escape of water when the gun is working, and a gunmetal valve immediately in front of the barrel block, which prevents the escape of water when the gun is not firing and the barrel home.
The steam tube consists of a fixed tube and an outer tube, termed the slide valve, so arranged as to slide freely along the fixed tube. In the fixed tube there is a hole near each end, and a third hole in the threaded portion in front, to connect with the steam escape hole which is bored in the solid part of the front end of the barrel casing. This tube is fixed into the solid end of the barrel casing, and is retained in position by a screw which, being kept in adjustment by a keeper screw, ensures that the third hole coincides with the steam escape hole. At the breech end it fits into a recess.
If the gun is fired with elevation, the valve slides backwards, and, closing up the hole at the rear end of the tube, prevents the water entering; at the same time it leaves the front hole uncovered, which, being above the water level, allows the steam to enter the tube and escape through the steam escape hole in the barrel casing. Similarly, if the gun is fired with depression, the valve slides forward and allows the steam, but not the water, to escape through the rear hole.
In the lower part of the barrel casing is the ejector tube through which the empty cartridge cases are ejected from the gun. The tube is fitted with a spring, which prevents the cases falling backwards into the gun.
The breech casing consists of two outside plates, a bottom plate which is riveted to them, and the rear cross piece, the whole being closed by a cover.
The outside plates are dovetailed into the barrel casing, and, together with the cover, are secured by means of a cover joint pin.
On the outside of the right hand plate there are the following fittings:—(1) a socket and stud for securing and supporting the buffer spring; (2) the resistance piece, and (3) the stud for the check lever. On the outside of the left hand plate are three studs for holding the fusee spring box, the rear one being on the slide mentioned below; there are also two other studs on this plate for fixing a shoulder piece to the gun if required. In both plates are slots partly closed by slides, in which the crank bearings move, and on the inside of both plates are solid cams which control the path of the extractor. Below these, and supporting the side plates, are rests, along which the recoiling portion travels.
Along the bottom plate lies the trigger bar, and underneath is a bracket to which the elevating gear is attached by means of the elevating joint pin.
The outside plates are connected at the rear end by the rear cross piece, into which they both dovetail; this piece is fitted with (1) hollow handles, which are also used for carrying oil, and are closed by milled heads, fitted with camel-hair brushes; (2) a firing lever and spring, the lower end of which fits into the trigger bar, while the upper end is provided with a double button for firing; (3) an automatic double-handed safety catch, which is so arranged that unless it is held up the firing lever cannot be pressed forward; and (4) a pivoted shutter, which, when moved to the right or left, uncovers an aperture through which (when the lock is removed and the crank handle vertical) the barrel can be inspected or cleaned from the rear.
The cover is fitted with (1) springs to ensure the extractor dropping on recoil; (2) a gunmetal block to keep the lock down when back, and (3) at the rear end, a lock to fasten it. On the upper surface is the tangent sight, consisting of a stem, a graduated plate and slide. Running through the centre of the slide is a pinion, the teeth of which work in the rack on the stem. A pawl is secured to the pinion by a fixing pin. On the under side of one end of the pawl are teeth, which engage in the circular rack on the slide.
When the slide is at rest the stud on the inside of the milled head (nearest the slot for the slide spring) bears on the stud on the pawl immediately over the teeth, being actuated by the slide spring, thus forcing the teeth into the circular rack. This keeps the slide stationary on the stem. On rotating the milled head, this stud is partly disengaged from the stud on the pawl, thus permitting a second stud on the milled head to press on one side of the V-shaped ramp at the other end of the pawl. This action releases the teeth sufficiently to permit the pawl being moved round the circular rack by the action of the stud bearing on one side of the V-shaped ramp on the pawl; this moves the slide along the stem. On releasing the milled head, the spring positions the cover, thus causing the stud on the pawl to become once more engaged with the stud on the milled head and force the teeth into the rack.
Recoiling Portion.
The recoiling portion (which is mounted inside the non-recoiling portion) consists of a barrel and two side plates which carry the lock and the crank.
The barrel is coated with copper to protect it from rust; the gunmetal valve referred to above, which prevents the escape of water to the rear, is fitted just in front of the breech end, which is formed in the shape of a block; this block has two studs, one on each side, called the barrel trunnions, by means of which the barrel is attached to the side plates.
The side plates are each provided with a hole to receive the barrel trunnions, and in the case of the ·303-in. gun, with hooks for engaging the recesses on the top of the barrel block; also guides in which the flanges of the lock move, which are enlarged at the rear end to act as crank stops; in addition each has a bearing, through which the crank passes, thus connecting the latter with the barrel; these bearings move in slots in the breech casing. The left side plate is fitted with a connecting rod spring to hold the connecting rod upright when the lock is removed, and the right side plate is fitted with a side plate spring near the barrel, to keep the extractor in its highest position when the lock is home. The left side plate is prolonged to the front, and has a recess in which the bottom lever of the feed block engages.
The crank is fitted with a connecting rod, which is free to rotate on the crank pin, and, outside the breech casing on the right, with a handle which has a curved projecting arm, and on the left with a fusee, to which is attached a chain.
The connecting rod is attached to the crank by means of an axis pin, called the crank pin, and is arranged to take the lock by means of an interrupted screw, thereby connecting the crank and the lock. The connecting rod is divided into two parts, enabling its length to be increased by inserting washers of varying thicknesses. By this means it is ensured that a firm pressure is kept on the base of the cartridge at the moment of firing, thus preventing separations.
On the left of the breech casing there is a strong spiral spring, called the fusee spring, the rear end of which is connected by the fusee chain and fusee with the crank; the front end is attached to the breech casing by means of the fusee spring box and adjusting screw, which passes through the front end of the fusee spring box, and through the nut at the front end of the spring.
The lock is attached to the connecting rod by the screwed head, and when in the firing position closes the breech. In this position it is held by the side levers, the crank (which bears against stops on the side plates), and the connecting rod, the joint being slightly above the horizontal, to prevent the breech being opened at the moment of firing. The lock has a reciprocating motion communicated to it by the rotation of the crank, and is kept in position during its backward and forward movements by means of flanges working in guides on the side plates, and, when at the end of its backward travel and clear of the guides, by the gunmetal block underneath the cover.
The extractor is moved upwards by means of the side and extractor levers, and when in its highest position, is retained there by means of the side plate spring; this ensures the hole for the firing pin being opposite the centre of the base of the cartridge when the lock is home. The upward and downward movements of the extractor are regulated by guide ribs and stops; the upper stop forms part of the lock casing, and the lower one is removable.
The feed block, which fits under the cover into a recess cut in the breech casing, is provided with a slide to which are attached two pawls with springs, for the purpose of moving the cartridges from right to left; the slide has a transverse motion given to it by means of two levers which are fitted together; the top lever has a slot which engages a stud on the slide, and on the bottom lever is a stud which engages in a recess in the left side plate; by this means the slide is connected with the recoiling portion. The feed block has also two stationary pawls, which engage under the belt and prevent it slipping backwards during firing. To facilitate the entrance of the cartridges, the feed block is provided with a band roller, and in addition has steel guides fitted above and below in the cartridge way, which ensure the cartridges coming to the exact position where they can be gripped by the extractor; they are prevented from being pushed too far through to the left by means of the cartridge and bullet stops, which are inside the feed block.
The gun is supplied with cartridges from a belt which passes from right to left through the feed block. This belt is formed by two pieces of webbing connected together by eyelets and brass strips of two lengths, the projecting strips showing how far the cartridges should be inserted; the belt is made thick at the edge next the bullets by being folded over a piece of cord, so that the cartridges may be kept parallel in passing through the feed block, and lie evenly in the ammunition belt boxes.
(Flexible steel belts are now being used. These fold into their box in sections, and by withdrawing a pin the unexpended portion can be detached and packed away immediately. They appear to be giving considerable satisfaction, inasmuch as “belt troubles” are practically impossible.)
Converted Guns.
Converted guns are the original ·45-in. guns made to take the ·303-in. cartridge.
The conversion consists in the substitution of ·303-in. barrels for the ·45-in. barrels and the adaption of the mechanism to the smaller calibre by the introduction of new parts or the alteration of existing parts.
The Mark II differs from the Mark I in being fitted with the service ·303-in. barrel and muzzle attachment for ball firing, whereas the Mark I has a special muzzle attachment and a heavy barrel. The difference in the barrels affects also certain other parts. In both Marks I and II converted guns the attachment for ball firing must always be on the guns, as, owing to the greater weight of the component parts, these guns will not work without it.
The tangent sight is graduated to 2,500 yards.
The weight is 64 lbs.
In other respects they resemble the ·303-in. gun except that the connecting rod is not above the horizontal and that there is a space of about ⅒ of an inch between the projecting arm of the crank handle and the resistance piece.
Ammunition.
All marks of ·303-in. ball ammunition may be used, but care should be taken to select ammunition of the most recent manufacture. Mark VII can, however, be used only in guns specially modified to take it.
Explanation of Plates I and II.
1. End of crank. 2. Projecting arm of crank handle. 3. Crank handle. 4. Breech casing. 5. Fusee spring } Dotted 6. Chain } lines in 7. Fusee } Fig. 1. 8. Spring box } 9. Resistance piece. 10. Buffer spring. 11. Check lever. 12. Lock casing. 13. Firing lever. 14. Trigger bar. 15. Projection on trigger bar. 16. Trigger. 17. Tumbler. 18. Lockspring. 19. Firing pin. 20. Crank. 21. Crank pin. 22. Connecting rod. 22A. Cotter. 23. Side levers. 24. Sear. 25. Extractor. 26. Barrel. 27. Ejector tube. 28. Horns of extractor. 29. Keeper bracket. 30. Side cams. 31. Cover spring. 32. Cover. 33. Gib. 34. Adjusting screw for fusee spring. 35. Extractor spring. 36. Handles. 37. Double button. 38. Trigger bar spring. 39. Gib spring. 41. Extractor levers. 42. Belt. 43. Upper extractor stop. 44. Groove for side plate spring. 45. Cartridge grooves. 46. Ejector tube spring. 47. Side plates. 48. Guides in which flanges of lock move. 49. Guide ribs for extractor. 50. Cover lock. 51. Gunmetal block. 52. Hole for firing pin. 53. Safety catch. 54. Screwed head. 55. Connecting rod spring. 56. Crank bearings. 57. Slots, breech casing. 58. Crank stops. 59. Ammunition belt box, No. 2. 60. Feed block. 61. Top lever feed block. 62. Cork plug. 63. Feed block slide. 64. Top pawl. 65. Bottom pawl. 66. Band roller. 67. Barrel casing. 68. Screwed plug for filling. 69. Asbestos packing. 70. Packing gland. 71. Cannelure for asbestos packing. 72. Gunmetal valve. 73. Steam tube. 74. } Holes in steam tube. 75. } 76. Slide valve. 77. Steam escape hole. 78. Milled heads of oil brushes. 79. Oil brush. 80. Sight, tangent. 81. Sight, fore. 82. Shutter. 83. Shutter spring. 84. Shutter catch. 85. Notch for shutter catch. 86. Screwed plug for emptying. 87. Slides, right and left. 88. Gib spring cover. 89. Check lever collar. 90. Cover lock spring. 91. Safety catch spring. 92. Tangent sight spring. 93. Bottom lever feed block. 94. Trunnions of barrel. 95. Extractor stop. 96. Firing lever spring. 97. Shutter pivot screw.
Plate I.
GUN MAXIM, ·303 INCH.
SIDE ELEVATION.
Plate II.
GUN MAXIM ·303 INCH.
PLAN WITH COVER REMOVED.