The firing mechanism consists of an ordinary pivoted hammer with main and sear springs. Cocking takes place automatically by heel-and-toe cams outside the right part of the breech, hut it can be done with the fingers, and the entire breech mechanism can be removed, whether the block be closed or opened. Except the 1-pounder and the mountain gun. all of this system are jacketed to stand a pressure of 18 tons. The projectiles have a travel of 35 calibers, which makes the gun about 4-4 calibers long. All guns above 1-pounders must exceed 2,000 ft. initial velocity, with black or brown powders ; 2,350 ft. being reached with smokeless powder.
Recognizing the great advantage of the rapid-fire system, and anticipating the large field of employment for a reliable and effective weapon of this kind. Lieutenants Driggs and Schroeder, U. S. N., took hold of the subject in 1887, and by careful study and experiment developed a weapon that has already met with favor among naval experts. The jacket is in two parts, one of which is termed a sleeve and is shrunk upon the tube, the two parts being connected under the trunnion band by the screw thread of the latter. The breech mechanism is in rear of the jacket, which forms its natural housing and protection. One of the most important features in the breech closure is the lightness of the block, which is further enhanced by revolving the block upon an interior axle. There are two independent extractors, either one of which will eject the empty cases.
The breech being closed and the gun fired, the operator revolves the handle through 90', which opens the breech, full-cocks the firing mechanism, and throws the empty oases well to the rear. The breech being closed, the block is supported by a cam which fits in a recess in the center of the block. Moving the handle around revolves the cam, forcing the firing pin to the rear and cocking it. The twist in the rifling is 1 turn in 30 calibers in the 1-pounder ; in the 3-pounder 1 turn in 100 to 1 in 25 calibers ; and in the 6-pounder 1 turn in 150 to 1 in 27 calibers. In tests for rapidity, the 6-pounder was fired eight rounds in 20 seconds. In testing for accuracy, all of 20 shots fell inside a lateral distance of six feet in 1.500 yards. The Nordenfeldt rapid fire guns were very similar in appearance to the Hotchkiss, and differed but in few particulars. The breech-wedge of the llotchkiss was in one piece, while that of the Nordenfeldt was in two. The former was capable of almost instantaneous pointing by means of a shoulder-piece, while the latter was pointed a little more slowly by means of screw gearing manipulated by two hand wheels. The former was mounted on a
non-recoil elastic frame stand, and the latter was mounted for short recoil. Since these pio neers, others have entered the field, the principal among them being Armstrong, Krupp, Gruson, Maxim, Thronson, Engstr3m (rig. 5), Canet, Dandelean, and Skoda. In general terms, the principal differences in these types are those per•tainin to details of breech mechan ism. The form of breech closure in each is either• that of a sliding wedge or of an interrupted screw, and, in all, the longitudinal strains arc taken by the jacket instead of by the tube.
The ingenuity displayed in the Maxim automatic gun is so remarkable that it deserves rather more than general notice, although it. may be outlived by a number of the other types. The gun is single-barreled, so arranged in its mounting's as to slide freely to and fm in its supports when firing. The first round is fired by hand, and the automatic system is set in motion by the resultant recoil as follows : The recoil opens the breech, withdraws a loaded cartridge from the belt, extracts the empty case, and cocks the hammer, at the same time stretching a spiral spring, which, when the recoil is absorbed• forces the barrel into the firing position ; the return of the moving parts expels the empty case, thrusts a loaded cartridge into the barrel, pushes a fresh cartridge in the belt into position, closes the breech, and pulls the trigger.
Almost, at the beginning of the recoil, a shaft and crank begin to rotate, and thus gradually draw all other movable parts away from the barrel. A sliding piece, which has an undercut groove on its forward face, exactly fitting the head of a cartridge, serves the double purpose of breech closure and carrier• for transferring cartridges from belt to gnu ; as it moves away from the barrel it withdraws an empty case front the bore and a loaded cartridge from the belt, and as its rearward motion eoutinues, it drops, partly by gravity, and partly by the action of a spring, into such a position as to bring the loaded cartridge into line with the barrel, and the empty case in line with the discharge (tube. In tests for durability, an average rapidity of 600 rounds per minute was obtained, the loading and firing mechanism working faultlessly.