Gerdom Rapid-firing Breech Mechanism.
The breech-block has two threaded and two plain sectors (each 90 degrees) with corresponding sectors in the breech of the gun, so that the block is locked or unlocked by a quarter of a turn. The block contains a firing-pin which, with its spring, is inserted from the front end of the block, which is then closed by a threaded cap. The centre hole in this cap permits the striking end of the pin to come through to the front in certain positions of the block and to hit the primer. The rear end of the block is countersunk to receive the operating-lever, the locking-latch and its spring, the cocking-lever and its hinge-pin, the trunnioned collar, the notched cap, and the sear and its spring.
The extracting-device engages in front of the cartridge-head and grips it for more than one eighth of its circumference. Its motion is guided parallel to the axis of the piece by two cylindrical arms working in slots cut in the breech. Swinging the carrier-ring around its pivot causes the extracting-device first to act as a wedge to loosen the cartridge-case, and then by a rapid motion the case is thrown out of the gun, or far enough to the rear in the breech to be easily removed by hand.
The operation of the mechanism of the gun is as follows:
The operating-lever is seized with the left hand, and a handle on the right rear face of the carrier-ring with the right hand. The lever is pulled slightly more than 90° to the left.
The first motion of the lever unlocks the cocking-latch; the remainder of the motion rotates the block in the carrier-ring, disengaging the screw-threads. During this motion of rotation the cocking-lever has pulled back the firing-pin, which is held in position by an edge of the sear engaging under a notch on the screw-cap.
The carrier-ring is then swung to the left by the handle in the right hand.
The block moves to the left with the ring and passes partly through the slot out of the breech and uncovers the bore.
The first motion of the ring loosens the cartridge-case, as before described, and then ejects it. The new charge is then thrown in, no care being taken to seat it; the ring swung to, and the block rotated and locked.
As soon as the block is locked, pulling the sear fires the gun.
FIXED AMMUNITION.
Smokeless powder will be used, about 1¾ lbs. forming the charge.
The shell, cast iron, weighs 16 lbs. and also contains a bursting-charge of 8 oz. of powder.
The shrapnel will be similar to the Frankford Arsenal shrapnel now manufactured, but longer and heavier (16 lbs. 10 oz.), and will break into about 240 pieces (balls and fragments).
The metallic case, brass or aluminum, has the projectile inserted in it to the distance of 1.75 inches, the base of the projectile being separated from the powder-charge by a felt wad. The total length of a round is 18.33 inches.
Experiments with charges of Troisdorf powder from 1 lb. 8 oz. to 2 lbs. 1 oz. have given with the 3.2-inch gun velocities from 1765 to 2032 ft.-sec.
Supplying Ammunition.—It is proposed to have boxes that can be readily opened and closed containing a certain number of rounds, about ten for 3.2-inch gun, carried by the supply-train. When a battery requires ammunition, the boxes will be taken from the ammunition-wagon, opened and the chests filled. The empty metallic cases with the battery are then placed in the boxes, which are securely closed, loaded on the ammunition-wagon and returned to the depot by the officer in charge; and are from there returned by the ordnance officer to the Frankford Arsenal to be again filled and prepared for service. The cost of supplying ammunition by this method will be less than it is now.
CHAPTER II.
3.2-inch Guns. Sights. Ammunition. Fuzes. Range Table.
3.2-INCH B. L. RIFLE, MODEL 1885 (MODIFIED). ([Fig. 38.])
| Material | steel |
| Total length | 7.56 feet |
| Calibre | 3.2 inches |
| Weight | 829 pounds |
| Grooves | 24 |
| Twist of rifling, uniform | 1 turn in 30 calibres |
| Axis of trunnions above ground | 3.56 feet |
| Powder-chamber | ellipsoidal |
| Vent | radial |
| Preponderance | 50 pounds |
| Muzzle velocity | 1685 ft.-sec. |
| Maximum range for shrapnel[4] | 6613 yards |
This gun consists of a tube (a), jacket (b), trunnion-ring (c), sleeve (d), key-ring (e), locking-ring (f), base-ring (g), and breech mechanism, De Bange obturator, vent-bushing of copper.
3.2-INCH B. L. RIFLE, MODEL '90. ([Fig. 39.])
This gun consists of tube (g), jacket (h), and breech mechanism, De Bange obturator, vent-bushing of copper.
The jacket, trunnion-ring, base-ring, and sleeve, of the model of 1885, form one piece, and the key-ring is omitted, as the tube and jacket are locked firmly together by shoulders (a, b, c) in rear and shoulders in front, with a projection on the tube that fits into a corresponding recess in the jacket.
d is the powder-chamber, f the slope from no lands to maximum lands, and e the connecting slope for seat of rotary band.
The vent-cover is a pin working in a slot in the face of the carrier-ring. (See [Fig. 36.])
SIGHTS.
Fig. 38.
Fig. 39.
Fig. 40.
The Front Sight ([Fig. 40]) is attached to the right rim-base, and consists of the base a, the standard b, and the cylinder c, all formed in one piece. The cylinder c is a bushing open at both ends, the interior being formed of two conical frustums c′ joined at their smaller bases and having at this junction cross-wires (+), d, of platinum, which give the exact centre of the sight. In the new sights the cross-wires of watch-spring are placed diagonally (X). The cross-wires are used with the peep of the breech-sight, and the point e on top is used with the open sight.
Fig. 41.
The Breech-sight ([Fig. 41]) consists of a tangent scale affixed to a circular base revolving in a plane normal to the axis of the piece to compensate for inclination of trunnions when on uneven ground. The scale moves laterally on its base to correct for wind and drift, and bears a spirit-level, f. Along the vertical limb, C, of the sight, which is slotted, moves an eye-piece, D, actuated by a screw, d. This eye-piece (bearing the peep-sight d′) extends on either side of the slot, the lower edge being horizontal and bevelled. The one on the right is graduated into ten equal parts. (The vertical limb being graduated into degrees (0 to 15°), and then sub-divided by diagonals into sixths, a diagonal scale of equal parts reading to minutes is obtained. The rear sights now being issued have range scales in yards for shell and shrapnel engraved upon the sight in addition to the degree scale. The scale of yards for shrapnel on the rear face of the sight, left side, is arranged with diagonal lines, to be read in the same manner as the degree scale. Each diagonal embraces 250 yards of range, and there are five divisions on the upper edge of the slide, by which this space is sub-divided, so that the intervals of 50 yards in range are read directly from the scale.
The scale of yards for shell, on the front face of the sight, is marked for each 100 yards of range, and is read from an index line on the slide.
The horizontal limb, or cross-bar, e, which is actuated by the screws e′e′, is graduated into spaces, each of which corresponds to a deviation equal to 1/345 of the range. (In future constructions this division will correspond to 1/1000 of the range.) This variation is tabulated in the range table under the heading "Deflection for one division of the horizontal scale."
By means of a pivot, B, the sight proper is attached to the stem A, the axis of rotation being at the zero of the scale. The stem tapers so as to fit into the sight-socket fixed at the breech. A pin projecting from the stem, and fitting in a recess in the socket, insures the sight being properly placed on the gun.
The sight is first levelled and clamped by means of the clamp-screw a before sighting. Vertical and horizontal changes for elevation, drift, etc., are given by the thumb-screws d and e′e′.
THE POINTING ARC.
(Fig. 41a.)
This instrument, now under consideration for use with field-artillery, to replace wholly or in part the rear sight, is made principally of bronze, and comprises the arc a, the slide b, and the level-piece c.
The arc has two small seating plates, d d, secured to its base by countersunk screws.
The slide is connected to the arc by a dovetail-joint, and moves over it, the friction of a spring keeping the slide in any desired position. The tension of this spring is adjusted by the two screws on the side of the slide.
Fig. 41a.
The steel pin on the under surface of the slide moves in the groove on the upper surface of the arc, and, by abutting against the steel stop-pins e at each end of the groove, prevents the slide from being moved off the arc. The arc is graduated from 0 to 20 degrees, but readings to 2 minutes are obtained by means of the vernier, f, at the rear of the slide.
Plates, graduated in yards for shell or shrapnel, are on either side of the arc. They are removable, being graduated for the piece with which the arc is used.
The zero index-marks on the sides of the slide are supplemented by two others equidistant, plus 2 degrees and minus 2 degrees. Any one of the three may be used in setting the slide to a desired range in yards.
The top of the slide has a scale, graduated 3 degrees on either side of the zero, with sub-divisions of 6 minutes; the markings plus and minus are the reverse of those on the side of the slide. The vernier, g, on the level-piece permits of a least reading of 2 minutes being obtained. Motion is given the level-piece by the deflection-screw h.
To set the pointing arc, make the zero of the level-piece coincide with the zero of the slide-scale, and then take the required elevation in yards on the side desired. Should the piece and object fired at be on different levels, and the angle known, the index of the level is moved to indicate this angle—to the plus side if an elevation, and to the minus side if a depression; then take the elevation in yards as before.
The correction is made in this way for 3 degrees or less, but for angles above 3, up to 5 degrees, the 2-degree marks on the side of the slide must be used, the index mark of the level being moved to coincide with the mark corresponding to the number of degrees—elevation or depression—less 2 degrees. The plus 2-degree mark is used as an index when the object has an elevation, and the minus 2-degree mark when a depression.
To obtain the angle corresponding to difference of level, sight the piece on the object by the ordinary sight, using any elevation; set the pointing arc at this elevation, and move the level-piece by the deflecting-screw until the air-bubble is centred. The index of the level-piece then points to the desired angle—plus if an elevation, and minus if a depression.
If the wheels of the carriage be not on the same level the gun will shoot towards the lower wheel. A correction for this is made by a deflection-scale.
The correction for deflection due to inclination of trunnions, expressed in units of the deflection-scale, is, at any range, equal to the product of the angle of elevation and the angle of inclination of the trunnions, both expressed in degrees, into a constant multiplier. When the divisions of the deflection scale are 1/500 of the distance between the sights this multiplier is 0.1523; when the divisions are 1/1000 it is 0.3046. The rear sight must be moved towards the higher wheel.