The foregoing named parts may be said to be essential to all breech-loading arms in which the metallic cartridge is used; the dif ferent ways in which they are combined mark the systems. These combinations have refer ence chiefly to the modes of operating and locking the breech-lock. The different sys tems may be classified into: (1) those with a fixed chamber; (2) those with a movable chamber. The latter have now become obso lete. The first class have (1) a movable barrel; (2) a movable breech-block. With each the motion may be sliding, in which case it moves in grooves; rotating when it swings on a hinge; or sliding and rotating combined. The greater number of systems belong to the class of a *movable breech-block rotating about an axis." In arms of this class the axis of motion may be parallel to the axis of the barrel, and above, below, or to one side of it; or perpendicular to that axis, being vertical or horizontal, and lying in or out of the plane of the axis. The position of the hinge has an important influence on the facility of oper ating the block, inserting the cartridge, and extracting the empty shell; the most suitable position is deemed to be in front of the centre of the block. In this case the motion of opening and closing the block is natural and easy; the cartridge is pushed into its place by the block, and a very simple retractor serves to withdraw the empty shell after firing. The most serious defect found in breech-loading arms was the escape of the flame through the joint, which not only incommoded the shooter, but, by fouling the machinery, seriously inter fered with its operation. At present this is entirely overcome by the elastic metallic case of the cartridge. The advantages of breech loading over muzzle-loading arms are (1) greater certainty and rapidity of fire; (2) greater security from accidents and loading; (3) the impossibility of getting more than one cartridge into the piece at the same time; (4) greater facility of loading under all circum stances, and particularly when the soldier is mounted, lying on the ground or firing from behind any cover.
The There are certain functions performed by, i and certain important condi tions to be fulfilled in the construction of, the different portions of a small-arm. The barrel is by far the most important part, its office being to concentrate the force of a charge of powder on a projectile, and give it proper ini tial velocity and direction; for these purposes, and for the safety of the firer, it should be made of the best material and with the great est care. In determining the exterior form, it is not only necessary to give such thickness to the different parts as will best resist the explosion effect of the charge, but such as will prevent it from being belt when subject to rough usage. Weight; to a certain extent is necessary to limit recoil, to give steadiness to the barrel in aiming, and to prevent it from *springing* in firing. The latter defect gener ally arises from bad workmanship, whereby there is a greater thickness of metal and con sequently less expansion on one side of the bore than on the other.
Three points are to be consid ered in determining the calibre of small arms: (1) it should be as small as possible to enable the hunter or soldier to carry the greatest number of cartridges; (2) to diminish the amount of ammunition required, and to pre vent the confusion liable to arise from a vari erty of calibres, there should not be more than two for all arms of the same service, viz.,
one for the rifle and the carbine, and one for the pistol; (3) this point relates to the force and accuracy of the projectile, and to the flatness of its trajectory. The introduction of the elongated projectiles afforded the means of increasing the accuracy and range of firearms, without increasing the weight of the projectile, simply by reducing the calibre, which diminished the surface, opposed to the air. Too great reduction of calibre, however, gives a very long and weak projectile; and be sides, the effect of a projectile on an animate object depends not only on its penetration, but also on the shock communicated by it to the nervous system, or upon the surface of contact. These considerations have led to a general reduction of calibre of rifles.
The grooves being for the pur pose of communicating a rotary motion to the projectile around an axis coincident with its flight, their construction will depend upon the form, dimension and material of the projec tile, charge of powder, and angle of fire. The points to be considered in determining the form of grooves for arms are range accuracy of fire, endurance, and facility of cleaning the bore. Experiment has shown that for breech-loaders these points are best attained by making the grooves broad and shallow, and with a rapid twist. The chamber being a receptacle for the charge, its shape is made to conform to that of the cartridge. Its diameter is made a little larger, and that of the bore a little smaller than that of the pro jectile. This facilitates the insertion of the charge, and causes the projectile to be com pressed and held firmly by the bands in its passage through the bore. The bottom of the grooves and the surface of the chamber are generally continuous.
The ism comprises the principal parts that are peculiar to arms loading at the breech. The functions of these parts are the opening, clos ing, and locking of the breech, firing the charge and removing the empty cartridge shell. These are the objects for the accomplishment of which the different systems are variously con trived, and with which alone they are con cerned. The most important conditions to be fulfilled in the arrangement of this mechan ism are: (1) the number of parts should be as few as possible, and all should be of the simplest construction; (2) the strength and union of the parts should be such as not only to resist repeated discharges, but the bursting of a cartridge case, which sometimes occurs • from defective material or workmanship; (3) the locking of the breech-block should not only be secure, but all the parts by which it is effected should work freely without sticking; (4) the parts should be so arranged that the hammer cannot strike the firing-pin until the breech-block is properly locked; (5) the ham mer should not necessarily rest on the firing pin when the piece is carried loaded; (6) the breech should be unlocked without the ham mer being brought .necessarily to full cock; (7) the working parts should, as far as pos sible, be covered from dust and water; (8) the extractor should be so arranged as to require no cuts or openings in that part of the chamber which surrounds the body of the cartridge case.