The gunsmith's manual

by J. Parish Stelle; Wm. B. Harrison

Another Method.—Another method to ascertain if a barrel be straight, is to insert a slip of card into the muzzle of the gun and then look through the bore to the light. If the slip of card be properly placed the “shade” can readily be seen. The card slip need not be more than one-quarter of an inch in width and in length to just fit the muzzle so that it will be retained in place. It must be placed with the edge of the card toward the eye.

Fitting Barrels Together.—When selecting a pair of gun barrels, preparatory to joining them for the purpose of making a double-barreled gun, it is necessary to ascertain if the barrels be of the same length, and have the same size at breech and muzzle, and also at points between the breech and muzzle. Nearly all shot-gun barrels are ground, or made some smaller at the centre of their length than at other portions. Any one who is not conversant with this may be somewhat surprised on placing a straight-edge along the side of a barrel, a common musket barrel, for instance. Place the straight-edge on the top or bottom side, as the right and left hand sides are flattened, near the breech, and, of course, on these sides the hollowing of the centre is not so readily observed.

As the musket barrel has been mentioned, it may be inferred that two of these barrels are to be joined together. The first step is to cut them off at either end, to make them of the length desired, for as issued from the armories for army use, the barrels are too long to make a gun to be handled with ease and convenience. If they are cut down to the length of thirty or thirty-two inches they will be long enough for sporting purposes. According to the weight of gun desired, cut from either end; cut off the breech if a light gun is wanted, or cut off the muzzle to make a heavy gun.

The first step after cutting off and truing up the ends of the barrels, is to select the two sides to be joined together and file these two sides flat, more at the breech and less at the muzzle, until the smaller diameters at the middle just touch each other, without being so filed.

When you have in this way both barrels flattened as nearly alike as possible and as straight as can be done by testing with a straight-edge, lay both barrels on a level surface, and see that the flattened places touch each other true and evenly. To know if the flattening has been done parallel with the outside flats at the breech (supposing these to be left on the barrels) place a small square on the same surface on which the barrels are laid, letting the upright arm of the square just touch the outside flat. If the square touch the flat alike from top to bottom, then the flats are parallel, but if there be an open space to be seen, then file away the flat to be joined until the square indicates that both inner and outer flats are parallel. Be particular in regard to this, as it is easier to correct the inner flattened surface than to make parallel the outer one.

If the same amount be taken from the breech as from the muzzle, the point of divergence will not be sufficient for accurate shooting. More must be taken from the breech to allow of this divergence to be extended a greater distance. The flattening at the muzzle does not require to be very great, yet must be done to some extent; but, as before remarked, this will depend upon the smallness or size of the middle portions of the barrel.

It is very doubtful if any two gunsmiths will agree as to the inclination of a pair of barrels. Perhaps it would be almost foolishness to insist on any definite or certain inclination, so that the converging lines would come to a point. As an instance, let the point of divergence be two and a half yards, it follows that at forty yards the right barrel, if the gun were rigidly held as if fixed in a vice, would throw its charge about six inches to the left of the mark, and the left barrel, vice versa.

Let it be supposed that two barrels are each thirty-two inches in length and one-sixteenth inch thick at the muzzle and three-sixteenths thick at the breech, it requires the difference four-sixteenths be multiplied by the times the length of the barrels are contained in the forty yards, this being forty-five, to ascertain what distance the point of the different lines are from each other. In this case it is eleven and one-quarter inches, or five inches and five-eighths of an inch from the centre or line of sight. It may be remarked that if the point of convergence be forty yards it will be productive of as good results, perhaps, as any other.

Joining Barrels Together.—After the barrels are fitted together so that they are parallel, touching each other their entire length and equally in a vertical line, the next thing in order is to fit the top and bottom ribs. Fit the lower thimble or pipe through which the cross-bolt goes and cut the under rib to fit both above and below it, as this thimble is soldered direct to the barrels, not to the rib. Mark along the sides of the ribs with a sharp scriber, so as to leave a distinct line on the barrels to indicate their location. File bright and smooth the parts of the pipe and ribs where they are to be joined to the barrels and tin with good soft solder. Also tin the barrels where they are to be joined, and where the ribs come in contact. This is easily done by using a clear charcoal fire and heating the barrels and ribs quite slowly. Use muriate of zinc for flux, and apply the solder with a common soldering copper. If the copper be quite heavy and well heated the ribs can be tinned from the heat of the copper, as there is no need of putting these parts in the fire. If the barrels be properly heated and the solder beaten out thin on an anvil, it may be rubbed on the barrels without the aid of the copper. When it melts and flows, wipe off the surplus with a woolen rag which has been slightly moistened with oil.

When the barrels and other parts are nicely tinned, let them cool, and then fasten them in place in the manner they are to remain with binding-wire. Put a rod of iron through the lower thimble, and also through the upper thimbles, if they are to be fastened at this time. The reason of putting in this rod is twofold: it serves to keep the thimbles straight with the barrels, so as to properly receive the ramrod, and at the same time tends to hold the under rib firmly in place.