_Finishing Muzzles of Gun-Barrels._—To shorten a barrel, the general custom is to cut it off with a three-square file, by filing a groove around it, or else saw it off with a hack-saw; the latter method being preferable, as by sawing completely through the barrel the piece is removed with no temptation to sever it by bending, as is often the case when cutting off with a file. [Illustration: FIGURE 29.] After the piece is removed use a tool like the one shown in Fig. 29, to square up the end. This tool has a cutting part an inch in diameter and about an inch long. It is turned smaller back of the cutting portion, to make it lighter or better to handle. A hole, three-eighths of an inch diameter, is made centrally in the cutting end, and in this hole are inserted iron or brass plugs made to fit, and the other end of a size to fit the bore of different guns. After the barrel is squared up, bevel the inner edge of the muzzle with the tool, Fig. 30, which is nothing more than a common “rose-head,” and is made with similarly formed cutting teeth. About sixteen teeth are sufficient for these tools. The rose head tool has the cutting end about an inch diameter and nearly the same length, one-half the length being taken up by the pointed cutting end. [Illustration: FIGURE 30.] _Old Method of Straightening Barrels._—The old-time method of straightening a gun-barrel was by means of a fine thread of black silk or a hair, which was passed through the bore of the barrel. This line was drawn tight by being stretched from two ends of a rod of wood or spring steel, the elasticity of which kept it taut, and the workman looking through turned the barrel round so as to bring the thread of hair into coincidence successively with every portion of the inner surface. If there existed any concavity in any part of this surface, the thread would show it by the distance which would there appear between the thread itself and its reflection in the metal.