Muzzle-loaders are of almost every variety of gauge, while breech-loaders are made of a limited number of sizes. The sizes of this class of guns are 8, 10, 12, 14, 16 and 20, and are limited to these sizes, there being no intermediate sizes. The 10 and 12 bore are mostly in use, the 12 being in especial demand. The calibre or bore of military guns during the Revolution was 75 hundredths of an inch, and has been reduced by successive stages until now it is but 45 hundredths. Down to 1856 the calibre of the Springfield musket was 58 hundredths. In 1856 it was changed to 50 hundredths or one-half inch; and again, in 1873, it was changed to the present calibre of 45 hundredths. _Bursting of Barrels._—Bursting of barrels may result from three causes: Poor quality of iron of which the gun is made; an excess of charge; or some obstruction in the barrel so as to form an air space between the charge and the obstruction. Of poor quality barrels, and excess of charge it is needless to make mention. The instances of bursting from obstructions forming the air space or chamber may be mentioned in military guns, firing the charge but neglecting to remove the wooden tompion from the muzzle of the gun. In sporting guns snow may accidentally get into the muzzle or a lump of dirt may “somehow” get in so as to fill the bore, and when the gun is fired, it will probably, yes, most certainly be blown off or blown open where the obstruction exists; the muzzle of a gun being thrust into water for a couple of inches or more will have like effect. The gas formed by burning the powder finds no outlet of escape, and the whole expansive force concentrates itself on the weakest portion of the barrel, and as a result it is forced apart. In good guns the portion toward the muzzle is the thinnest, and obstructions are generally at or above this place, and it is in this proximity where most guns are burst. If within three, four or five inches from the muzzle, the portion so destroyed can be sawed off, the barrels squared up and it will not always seriously affect the shooting of the gun. In loading a gun be careful that there be no air space left between the charge and the ball or shot cartridge. In double guns, frequent firing the right barrel, which is the one fired the most, the recoil will often cause the ball or shot charge in the left barrel to be thrown forward from the powder, and when it is fired may either strain or burst the barrel. Even if there be a small air space between the powder and the ball or shot cartridge it will affect the shooting. Every one using double guns should accustom himself to the use alternately of both barrels, not only for safety but for good shooting. A barrel is often said to be a poor shooter, when its bad qualities may be wholly ascribed to the air space produced above the powder by the recoil occasioned by firing the other barrel.