Boring Gun Barrels.—The tool used for this purpose consists of a rod a little longer than the barrel to be bored, with a cutter head at one end. This cutter is about one-half or three-quarters of an inch long, and of a diameter a little larger than the bore that is to be enlarged. It can be made to be pulled through the barrel or to be pushed through when cutting. In the armories where many guns of the same calibre are made, a portion of the shank, next to the cutter, is made of the bore of the barrel, and the cutter made of the size the bore is to be enlarged. The portion that fills the bore acts as a guide, so that the cutter is forced to follow after it, and the enlarged bore is in the same line as the boring previously made. The cutting edges of the tool are, of course, next to the enlarged portion. As the tool is pulled through the barrel, the cuttings are left behind it as it advances; oil is to be supplied while cutting, and care must be exercised not to let it get clogged with cuttings, as a tearing of the surface of the barrel would be the result.
When the tool is made to be pushed through while cutting, the cutting edges of the tool is on the end, and it operates like a reamer. This cutting end should be bevelled off so as to follow the bore to be enlarged.
How to make Cutters for Boring.—One way to make these cutters is like a many-fluted reamer, with five, seven, or more cutters. The odd numbers will operate better than even ones. If made with too many cutting edges, there will not be clearance enough for the chips, and clogging will be the result. Then again, the cutters must not be too long, or there will be too much friction, and the barrel will become very hot in working. Also, if the friction is too great, the barrel may be bent and sprung in consequence.
One form of cutter is made like the cherry to make an elongated bullet, or like the cherry of a Minie bullet. They may also be made in form of an egg. A common twist drill welded to a steel rod has been used for small bores. A small fluted reamer welded to a rod will do where the enlarging is quite small. When the tool is to be pulled through the cutter may be made like a short twist drill not over an inch long, with the cutting edges next the rod, and not on the end, as these drills are generally made.
Quick-Boring Gun Barrels.—The way to bore gun barrels by hand is this: Make a steel rod with a square bit about six or eight inches long on one end, and a little less in diagonal diameter than the bore of the barrel. The whole rod should be a little longer, say a foot or so, than the barrel to be bored. Harden and temper the bit end. See that it is true and perfectly straight when ground. The grinding should be done by drawing the bit across the face of the grindstone, and this will leave the sides of the bit a little hollowing, and the edges quite sharp. Pack up one side with a thin strip of soft pine until it will just enter the breech end of the barrel. By means of a strong bit stock, or a handle affixed like an auger, turn it around, at the same time forcing it toward the muzzle, until it has cut its way through the entire length of the barrel. While the cutting is going on keep the interior of the barrel plentifully supplied with good oil. Now, as the bit will be a very little smaller than the bore of the barrel, remove it and take off the little strip of wood and place between it and the bit a strip of writing paper of the length and width of the side of the bit where the wood was placed; then insert the bit again at the breech and bore through to the muzzle. Repeat the operation again by inserting a second slip of paper, and so proceed, using plenty of oil, until the bore or calibre of the barrel is sufficiently enlarged.
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.
Freeing Gun Barrels.—It is often desired to free a barrel at the muzzle, or at both breech and muzzle; and the amount to be removed is so very little that it is hazardous to insert the boring bit for fear of removing too much. It is easily accomplished in this manner: Select a straight wood rod that does not quite fill the bore of the gun and saw a slit with a fine saw at one end, for about three or four inches, and parallel with the length of the rod. Cut strips of fine emery paper, or emery cloth, the width of which should be the same as the length of the slot, insert one end in the slot and wrap the projecting part around the rod, introduce this end into the barrel and work it up and down, if it be desired to finish the barrel that way, or turn it around by means of a bit stock or lathe if the finish is to be thus done.
Many gunsmiths cast soft lead at the end of a rod, using the muzzle of the gun as a size mould, and after removing from the barrel, apply oil and fine emery, and with this work the inside of the barrel.
Figure 28.
Another Method.—There is another plan. Make a rod of soft pine wood that almost fills the bore and make a small hole, say about one-eighth of an inch diameter at the point where the saw kerf is to terminate. Cover this portion of the rod with good glue, made thin, and then roll it in the emery, the same as making an emery wheel or a buff-stick. When dry use it in the same way as the other forms of rod. When desired to increase the size, which will be necessary, a thin wedge can be inserted in the saw-kerf and pressed deeper in as the bore increases, or near as the rod diminishes its size. By wrapping the rod with fine twine where the hole is made there will be no danger of splitting the rod when the wedge is pushed in. The same form of wedge can be used in the rod first described, and at the same time the wedge will help keep the emery cloth or paper in place. The cut, Fig. 28, shows the rod as ready to receive the coating of emery.
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.
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.
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.
The New Method.—There is another process of straightening barrels which was explained by a writer in a scientific paper a few years ago, which is termed “straightening by the shade,” and by this method barrels can be straightened with a greater degree of precision than by any other known process. The principle is something like this: If we examine a plane mirror for the purpose of ascertaining whether its reflecting surface is a true plane, we cause objects to be reflected from it to the eye at small angles of incidence. If under these circumstances every part of the mirror gives an image true to nature, he pronounces it perfect; for the slightest deviation from a true plane would cause a manifest distortion of the image. In the process of straightening barrels by the shade, crooks in the bore are detected upon the same principle. The internal surface of the barrel is a mirror, and whatever objects are reflected to the eye from any portion of it that lies beyond a certain distance, will be reflected under very small angles of incidence. As the interior surface of the barrel is not a plane mirror, the reflected image will not be true to nature. If the bore be straight, the image will have a normal distortion, which is due to the transverse or cylindrical curvature of the mirror; while if there be longitudinal flexures or crooks, there will be an abnormal distortion of the image, which will reveal the defect.
Figure 31.
When the eye looks into a gun barrel the interior surface appears to be spread out into a plane circular disk, as far from the eye as the other end of the barrel. Through the centre of this disk is a circular orifice, and surrounding this at equal distances from it and from each other, respectively, are several well-defined concentric circles, dividing the disk into as many bright concentric rings, each of an apparent breadth, precisely equal to the diameter of the central orifice which is the other end of the bore as seen by direct vision. The several concentric circles are so many images of the end of the bore reflected to the eye from different points along its length. The first of these circles, or that nearest the central orifice, is an image formed by light once reflected. The second, third, fourth, etc., respectively, are images formed by light reflected two, three, four, times, etc. In order to see how these images are formed, and to find their respective points of location in the bore, consider that a ray of light from each point in the end of the calibre, as shown at a, Fig. 31, may pass to same point b, on the other side of the bore, and be thence reflected to the eye, thus forming at b, an image at the end of the bore, of one reflection. Another ray from the same point may pursue the route a, c, d, e, forming an image at d of two reflections. Another ray may take the route, a, f, g, h, e, forming an image at h by three reflections, and so on for the other images since in the formation of each of these images, respectively, the angles of incidence and reflection are equal, it follows that the focus, or point of place of the image b, formed by one reflection of light, is at one-third of the distance from the eye to the further end of the bore; that formed by two reflections d, is one-fifth; that by three reflections is one-seventh, and the succeeding ones, one-ninth, one-eleventh, etc., of the same distance.
Therefore, it will be observed that all these images are located within the third part of the length of the bore nearest to the eye. Consequently there are two-thirds of the entire length of the bore in which none of these images appear. It is to this part of the bore, only that the workman directs his attention, for it is here only that he can cause the “shade” to appear which discloses the crooks in the bore if any exist. When this part is straightened, he inverts the barrel and works from the other end.
Figure 32.
The practical application of the process is made in this manner: the workman has a rest, generally consisting of an upright strip of board of convenient height with a V cut in its upper end for convenience in resting the barrel in case of rotating it. Across a window opposite, at almost any distance, say about ten or twelve feet, is nailed horizontally, a strip of board like a common lath, as the horizontal bar of the window sashes where they come together at the middle of the window (provided there be upper and lower sashes) will answer nearly as good a purpose. Now place one end of the barrel in the V of the rest, look into the bore, directing the eye to the lower side of it and to the point just beyond the image b; gradually depress the end held in the hand, bringing the direction nearer and nearer to the horizontal strip, or the sash bar as the case may be, and a dark shade is soon seen as shown at m, Fig. 32. This is the reflected image of the horizontal strip, or sash bar, the curved part of the outline being the image of the straight-edge. Depress the end more and more and the shade lengthens to n, o, p, etc. If the bore be perfectly straight, the shade will always maintain a true and symmetrical parabolic form, growing more and more pointed at its apex, until it reaches the further end of the bore. But if there be even the slightest flexure or crook in the bore the parabolic figure of the shade will be distorted. If a distortion be discovered, the barrel is slowly revolved about its axis as it is retained in the rest; at the same time slightly elevating and depressing the end held in the hands, until the shade assumes a form in which the two sides near the apex are equally drawn in toward each other as shown at q. If the crook be considerable the two sides may be drawn quite together, cutting off a portion of the shade of the apex as at r. This tells that there is a crook at q, and also tells that the bore is concave downward at that point. It will require some experience to tell how far that point is from the eye, but when that is learned, the fore-finger placed upon this point on the under side of the barrel tells where the blow must be given to straighten it as it ought to be.
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.
Before fastening the parts with binding wire, fill the space between the top rib and barrels with small pieces of solder, or what is better, a small rod of solder like a wire, but not large enough to interfere with the rib fitting close to the barrels.
Soldering Barrels Together.—Now begin to carefully heat the work, commencing at the breech, and when sufficiently hot, don’t heat too fast nor too hot, apply solder, using the muriate of zinc as a flux, to the joinings of the ribs and barrels. If the solder be hammered quite thin it will be readily melted by the heat of the barrels, and will be “sucked in” until the space between the different pieces is completely filled. Proceed carefully in this way until the entire length of the barrels is gone over. Turn the work often in the fire, so that all portions are evenly heated. At the muzzle fit and insert a small piece to fill the interstice between the barrels and the top rib.
It is necessary that all the space between the top rib and the barrels be completely filled with solder, or rust will form there, which will prove of serious detriment to the barrels, and in time work under the ribs, throwing them from the barrels if even a little torsion or springing of the barrels should ever take place.
During the progress of soldering, see that the parts are kept pressed close together, and that they do not spring away from each other by their expansion during heating. A small iron clamp screw placed at the breech and also one at the muzzle, is very convenient, as by tightening the screw there is less danger of the parts springing apart. When the breech is soldered and somewhat cooled, the clamp there placed can be removed. These clamps, made of malleable iron, can be obtained at the hardware stores.
When the work is soldered and is cool, wash it well with warm water, using a stiff brush to remove dirt and all traces of the acid flux that may remain on the work. With a chisel or scraper remove all superfluous solder and brighten the work with emery cloth or paper of different grades. Begin with the coarser and finishing with the fine or with flour and emery.
Why not Braze Barrels?—It was formerly the practice to braze barrels together, with spelter solder, at the breech or at both breech and muzzle, but good workmen condemn the practice, as heating the barrels to a high heat in order to melt this solder somewhat diminishes the strength of the metal, and as it is also necessary to again clean and brighten the work after brazing, and to perfectly brighten the flats where they lie together is not so easy a matter. In the life of the gun, it was found to be of no real benefit to thus braze them, as the parts were securely held in place if well soldered with soft solder, and of late years but very few barrels have been thus brazed.
Select solder of good quality, put the work well together, and the barrels will remain firmly and rigidly in place, and will not be separated except by unfair means.
Percussioning.—The term Percussioning is used to designate the operations of drilling, and finishing the cone or nipple seat, tapping, putting in the tube or cone (by some called nipple) and otherwise finishing up the parts bearing relationship to the cone seat.
The first operation, after ascertaining the locality where to drill the hole for the nipple, is to drill this hole. If a double gun the nipples must be inserted as near the centre of the breech as possible to get them and have a direct communication, with no unnecessary angles, in the passage-way of the flame of the cap to the powder in the chamber. From the bottom of the hole drilled for the nipple a small vent, as small as can conveniently be made, must or ought to communicate directly to the powder chamber. The nipple ought to be seated or screwed to the bottom of the hole and the vent be an unbroken continuation of the opening through the nipple. Let there be no chamber or reservoir between the bottom end of the nipple and the bottom of the hole in which it is screwed.
Figure 33.
But to return to the drilling. From the axial or central line of the barrel, this hole must be drilled at an angle of forty-five degrees so that the nipple when inserted shall stand at that angle. In the cut Fig. 33, a represents the central line of the barrels, b a line at right angles to this, and c the angle of forty-five degrees. If the workman have no lathe and is necessitated to use a bit-stock or breast drill, a piece of iron can be fitted to lay upon the barrels with one end elevated three or four inches with the end turned at an angle in a hole drilled in this end to receive the drill, which should fill the hole. By clamping this upon the barrels, inserting the drill in the hole and having a prick mark where the hole is to be made for the nipple, it forms a reliable guide to insure the correctness of the hole, and also to get any number of holes alike. To insure the hole to be tapped or threaded properly the guide can be kept in position and the hole tapped after being cupped to form the seat.
If a lathe be used to drill the hole, a piece of wood or an iron forging can be fitted to the spindle against which the work is held and when made of the proper angle and the barrel confined upon it to drill the hole, no guide is necessary, as the drill being held in the spindle and the spindle running in its bearings operates upon the same principle as the guide clamped upon the barrels. An upright drill can be fitted with a forging or casting to hold the barrels in the same manner.
The size of hole to be drilled ought to be that of the smaller sized nipples, as in time frequent re-tappings to insert new nipples will enlarge the hole. Perhaps a broken nipple may necessitate drilling or cutting out and the thread may be injured somewhat, so that it may have to be bored out and a new thread made to receive a larger nipple.
Figure 34.
After the hole is drilled it is cupped or a seat formed for the shoulders of the nipple to rest upon. This is done with the tool shown in Fig. 34. The guide is used to get the proper angle of this seat, the same as in drilling. The stem at the end of the cutting portion of the tool, enters and fills the hole drilled, which insures the correct formation of the seat. The tap is held in the guide in the same manner and it follows that the thread has been made at the same angle that the hole was drilled.
Finishing Nipple Seat.—The filing and finishing of the nipple seat is one in which tastes differ or the price of the work may demand. This hint may be given, the seating tool must cut a seat large enough to receive the nipple and in filing keep this seat full size, taking care not to allow the file to take away or reduce any portion of it. A study of this portion of different guns that may come under the observation of the workman is the best guide for forming and shaping these parts. The first effort may be to form a nipple seat from a piece of hard wood shaped like the barrel with its lump, using the drill, the seating tool and even the tap, then finish up with files, as if it were iron, and insert the nipple. Better to correct a fault in a “sham” of wood than spoil a good barrel breech.
The Vent, in Percussion Gun Barrels.—When the old flint-lock was pushed to one side by the introduction of the percussion principle, it was thought by many that there was a difference in shooting and that the flint-lock shot “smoother” than its substitute. In the percussion gun there was thought to be more recoil than in the other form of gun. It was supposed that the hermetically closing of the breech, as the firing took place, was the cause of this, and to remedy the matter a small vent was drilled near the locality of the vent or “touch-hole” of the old-time arm. A few gunsmiths and many users of arms cling to the vent and could “not do without it.” Some claim that this vent is of use, as it enables air to circulate through the barrel, after the ignition of the charge. While both these theories are doubted by others, one thing is quite certain, it increases the certainty and also aids the rapid ignition of the charge, as the air contained among the powder and held there in a more or less state of pressure, being so forced and held by the wadding, retards in some measure the entrance of the fire from the percussion cap. The vent allows this confined air to escape, and that is the only real and apparent good that can be accredited to it. In making these vents make them very small, and in no instance let them exceed a thirty-second of an inch. To prevent their being closed by rust or the debris of burnt powder, drill a larger hole, tap a thread in it and screw in a silver wire and then drill the vent through the wire after it has been finished to conform to the shape of the parts adjacent.
The Patent Breech.—The patent breech has been the subject of much discussion and much experimenting, some experts claiming one form to be superior to others, and then again there are those who set the patent breech aside and claim that the old flat-faced breech-pin is as good as any ever yet made. The formation of the base of the breech-loading shell has been called up as evidence in favor of the latter claim. The two forms are called in question, and then the query is made, “Does not the breech-loader shoot better or as well as the patent-breeched muzzle-loader?” But the patent breech is in favor with the mass of those who use the muzzle-loader, and no doubt has its advantages. The attempt has been made to form the interior base of a cartridge for breech-loaders upon the model of the interior of a patent breech, but thus far has not come into very extensive use.
Form of the Chamber or Cup.—While many forms of the chamber or cup of the patent breech are in use, the most simple form, and the one easiest to make, is that of an inverted elliptical cone. This form may be represented by the shape of an acorn if it were cut off even with the top of the cup. The shape is also one that will not weaken the breech nor affect the strength of the thread where it enters the barrel. The tool to shape it is easy to make. Turn a piece of steel the exact shape the “cup” is to be and then make a cutting tool of it by filing a groove on two sides, exactly like a flat drill of the required elliptical form, but with a “bulge” or cheek left on each side, and then file a groove mid-way in this cheek from point to base, and make it so as to form two cutting edges on each side of the cut first made. Each prominent part must be formed into cutting edges, like the cutting edges of a conical-shaped cherry to cut out bullet moulds. The cut, of bullet cherry, Fig. 71, Chapter XXVII, shows the way to make this tool.
With this form of “cup” there is great solidity of breech, and there need be but little fear of miss-fire or hang-fire in shooting, if the gun be properly loaded.