There are certain functions pe,-formed by, 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 of a firearm, its office being to concentrate the force of a charge of powder on a projectile, and give it proper initial velocity and direction; for these purposes, and for the safety of the firer, it should be made of the best material and with the greatest care. In determining the exterior torm, 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 bent w hen 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 generally arises from bad workmanship, whereby there is a greater thickness of metal, and consequently less expansion on one side of the bore than on the other. In some sporting rifles the barrel weighs from 12 10 15 lbs.
Three points are to be considered in determining the caliber of small arms: 1st. It should be as small as possible to enable the hunter or soldier to carry the greatest number of cartridges. 2d. To diminish the amount of am munition required, and to prevent the confusion liable to arise from a variety of calibers, there should vot be more than two for all arms of the same ser vice, viz., one for the rifle and the carbine, and one for the pistol. 3d. This point relates to the force and accuracy of the projectile, and to the flatness of its trajectory. The introduction of the elongated projectiles 4fforded the means of increasing the accuracy and range of firearms, without increasing the weight of the projectile, simply by reducing the caliber, which diminished the surface, opposed to the air. Too great reduction of caliber, however, gives a very long and weak projectile, and besides 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 surtace of con tact. These considerations have led to a general reduction of caliber of rifles.
The grooves being for the purpose 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 projectile, 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 larg-er,
and that of the bore a little smaller than that of the projectile. This facilitates the insertion of the charge, and causes the projectile to be compressed and held firmly by the lands in its passage through the bore. The bottom of the grooves and the surface of the chamber are generally continuous.
The breech-mechanism 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 car tridge shell. These arc the objects for the accomplishment of which the differ ent systems are variously contrived, and with which alone they are concerned, The most important conditions to be fulfilled in the arrangement of this mech anism are: ist. The number of parts should be as few as possible, and all should be of the simplest construction. 2d. The strength and union of the parts should be such as not only to resist repeated discharges, but the burst ing of a cartridge case, which sometimes occurs from defective material or workmanship. 3d. The locking of the breech-block should not only be se cure, but all the parts by which it is effected should work freely without stick ing. 4th. The parts should be so arranged that the hammer cannot strike the firing-pin until the breech-block is properly locked. 5th. The hammer should not necessarily rest on the firing pin when the piece is carried loaded. fith. The breech should be unlocked without the hammer being brought nec essarily to full cock. 7th. The working parts should, as far as possible, be cov ered from dust and water. 8th. The extractor should be so arranged as to re quire no cuts or openings in that part of the chamber which surrounds the body of the cartridge case. The lock is the tnachine by which the charge in the cartridge is ignited. Those of the present day belong to the percussion class, in which fire is produced by a blow upon the fulminating powder, con tained in the cartridge case. Locks are divided into side and center locks, depending upon the position occupied in the stock; each of these may be either front action, wherein the mainspring is in front of the tumbler, or back-action, where the spring is in rear of the tumbler. The mortise, which forms a bed for the lock of the latter construction, seriously affects the strength of the stock at the handle, and for this reason the front-action lock is generally pre ferred for all arms, except revolvers. The conditions to be fulfilled in the con struction of a lock are simplicity, strength, certainty of action, and freedom from such accidental motion of the parts as might produce explosion of the charge in the barrel.