Proving the Size during Boring.—A method of proving the size of the interior of the barrel and at the same time test its being perfectly of the same size throughout, is to cast an ingot of lead about an inch long in the muzzle, and with a rod forcing it through.
If the work be well done the interior of the barrel will present a bright mirror-like appearance, and will need no further finishing.
Draw-Boring.—Draw-boring is done with a rod that nearly fills the bore of the gun, and at one end of this rod is fitted a tool made like a short piece of file, but with the teeth made a great deal coarser and larger. This tool may be about an inch long, and of a round form on the cutting side, to fit the curvature of the bore. This tool is put on the end of the rod and worked back and forth, also turning it around, so as to present the cutter to all sides of the bore in which it is to operate. When it will cut no more the cutter is removed from its seat, a slip of paper put under it, and it is put in place and the operation repeated, and so continued until the bore of the gun is sufficiently enlarged.
Pieces of thin files, broken to length and with the ends ground to fit the rod, have been used for draw-boring, but the best and most effective tool is a bit of steel filed up to shape and properly fitted. One half of the cutting teeth should point forward and the other half backward, so that the cutter will remove some of the metal as it works in either direction, forward or back. If the cutter be an inch long, about three or four teeth may point one way, and as many the reverse direction.
In using these tools, keep them well oiled, to prevent tearing into the metal.
Choke-Boring.—The method of making a choke-bore is similar to quick-boring, except the cutting end of the rod does not go quite through the barrel, being withdrawn and again inserted with a slip of paper placed between the slip of wood and the cutter. This is worked not quite so far as the previous boring, being withdrawn and another slip of paper placed between the wood and the cutter, and this is worked in as far as desired. Care must be taken that the choke be gradual and even. A finish can be given by folding a piece of fine emery cloth or emery paper around a rod, and by turning this in the barrel, equalize any unevenness that may occur.
To enlarge the interior of a barrel, boring it choked at both breech and muzzle, push the rod to the distance from the breech the enlarging is to commence, and then commence boring, leaving off where the muzzle choke is to commence.
If the bore of a barrel is made to taper from muzzle to breech, it will scatter. If made to taper too much from breech to muzzle, it will compress the shot, and by so doing mangle or deface them so that they will “shoot wild,” while at the same time the effect on the gun will be to spring the barrel, and, if it be thin at the muzzle, as generally made, there is danger of enlargement of the bore at this portion of it.
Choke-Dressing a Gun Barrel.—A very slight variation in the size of the bore of a gun-barrel at one of its ends often has a marked effect on its shooting. In case where a shotgun is disposed to “scatter” too much, the remedy lies in enlarging the bore at the breech. Choke-boring would be the means resorted to where such an operation was convenient; but where not, choke-dressing may be made to answer a very good purpose. This consists in dressing out the breech with fine emery paper or cloth, wrapped upon a round wooden rod. A little oil should be used in finishing the dressing, which need not extend above half the length from the breech to the muzzle. No particular attention need be given as to the slope, as the size of the bore, under this operation, is sure to be left largest at the breech.
Barrels most Suitable for Choke-Boring.—Laminated steel barrels are the most suitable for choke-bore guns, being harder and more tenacious than Damascus, and, therefore, resist the repeated strain of heavy charges better; they will be found to be more durable, and lead less than barrels of softer material. Barrels of plain steel, or decarbonized steel, so called, should never be used for choke-bore guns, as they are unsafe for guns with light muzzles. Decarbonized steel is most suitable for rifles, where great strength of metal is employed. The finest pattern in Damascus is not always desirable, as the excessive twisting necessary to make the fine pattern often weakens the fibre of the metal.