The new eight inch converted muzzle-loading rifle is made on what is known as the "Pallisser System"; that is converting a smooth bore into a rifle by inserting a wrought iron tube at the muzzle.
In this paper I propose giving a brief description of how this change is made.
The original eleven inch S. B, is placed in a lathe and bored out to a diameter of 13."5 from the muzzle to the bottom of the chamber a distance of 131."2; the corners at the bottom being rounded oft with a radius of 1."7. The bore is very accurately gauged along its entire length and a plan made by which to turn down the outside of the tube. A course rounded screw thread is cut in the muzzle of the casing for a distance of 3."75 for the muzzle ring; and a further distance of ".5 without any thread, to insure the ring holding the tube close home. There is a small hole or gas escape ".2 m diameter, through the base of the breech from the right side of the cascable to the middle of the bottom of the bore, which is in connection with radial grooves cut on the bottom of the cup and tube, one of which joins the end of the spiral gas escape cut around the reduced portion of the A tube. The old vent is closed with a wrought iron screw plug, and the lock lugs on both sides removed, as it is intended to fire the gun with friction primers. A hole 1."5 diameter is bored in the chase at about 17." From the right rim-base for a screw steadying plug. As it was found that the gun when converted had a muzzle preponderance, the original cast iron trunnions were turned down eccentrically and a composition eccentric collar put on, the collar being secured to the trunnion by a screw key; the whole shifting the centre of support 1."5 further from the breech and giving the finished gun a preponderance of plus three hundred pounds at the base ring. The finished gun weighs seventeen thousand, three hundred and thirty pounds. The lining of the gun may be properly divided into three parts viz. A tube, B tube, and cup at the bottom of the bore.
The iron of which the tubes are made is obtained from the Ulster Iron Works at Saugerties N.Y., and is made from the best pig iron selected from magnetic and hematite ores taken from the mines of New Jersey and Lake Champlain. The pig iron is puddled for the purpose of purifying it from carbon, sulphur, silicon &c., four different kinds of iron being mixed in the furnace. When the mass is sufficiently purified and becomes pasty, it is separated into balls and passed under a steam trip-hammer, where the slag is removed and the ball formed into a bloom. The bloom is about 18" long, 4" or 5" square and weighs about one hundred pounds. This operation is very carefully watched, and balls showing any inherent weakness or want of proper puddling are rejected.
The blooms are then re-heated, rolled into slabs, cut into short pieces, piled, raised to a white or welding heat and again rolled into slabs. This process is repeated three times, great care being taken each time to maintain the fibre of the iron always in the same direction. The last pile from which the bar is finally rolled is composed of seventeen slabs, 51" long, 7" wide, the top and bottom slabs each ¾" thick and the intermediate ones 2" thick, making a pile 51" x 10" x 7". This pile is placed in an anthracite furnace, raised to a welding heat (3000° F.) and passed through a succession of rollers of gradually diminishing dimensions until it is finally rolled into the bar required for making the tube. The cross section of the finished bar is nearly, but not perfectly, trapezoidal, the sides bulging out slightly. By making the bar simply trapezoidal in cross section, it was found that, in coiling, the sides became concave, thereby forming a pocket, which in the subsequent coil welding served as a receptacle for cinder and prevented a perfect weld. In order to avoid this the shoulders were added whence a supply of metal could be drawn to fill up the concavity of the sides.
The bars are 18' long, 4" outside, 3 ¼" inside, 3 ¾" across the shoulder and 3 ½" deep. When the bar is subsequently wound around the shaft, narrow side inwards, the inside expands, the outside contracts making the bar 3" ½ square. The slabs in the bar stand vertical in the direction of their length and in the coil welding which takes place on the side of the bar and against the flat of the slabs, they are driven more solidly together. The iron of the bars breaks at a tensile strain of fifty thousand pounds per square inch, and presents when fractured a bright fibrous appearance indicating great tenacity.
The bar to be formed into a coil is about 34' long, being made up of two of the original bars welded together with a tongue weld. This tongue weld, or V scarf as it is sometimes called, by affording a firm grasp to the ends and by exposing a large surface for welding is thought to insure a strong joint; yet so great is the strain thrown on the bar in the operation of coiling, that separation does sometimes take place at this point. The weld is made in three heats. In the first, one end of the bar abuts against a heavy timber, and the other end is struck several blows with a sledge hammer to close and upset the joint. It is then twice heated and welded under a steam hammer, the hammering being on the sides. At the last heat the trapezoidal shape of the bar is restored by wedges between the bar and the hammer. At the same time the ends of the bar are tapered, and the end that is secured to the shaft in coiling is hammered into a knob and a hole punched in the end to hook a chain to, by which it is drawn from the furnace.
The furnace in which the bars are heated is 60' or 70' long, about 3' wide and 4' high, with seven fires on one side and the chimney at the end farthest from the coiling shaft. The bars being heated to a good red heat and drawn out and wound round a shaft 6 ½" diameter at the larger end and slightly tapered to facilitate the removal of the coil. The shaft is placed directly in front of the furnace, and has geared to it a feed screw carrying a block with a square hole cut in the top through which the bar passes. On the larger end of the shaft is a small ring or plate, in the side of which is a square bolt. The bar, when withdrawn from the furnace, is passed through the square hole in the block, under the shaft, and driven with a hammer between the square bolt and the shaft, close against the plate. The knob prevents the bar from drawing out. The shaft and feeding screw are revolved by a small engine, and the bar passing through the hole in the block, which is moved by the screw, is fed along the shaft. The coils are all left handed. When the whole bar has been coiled the shaft is lifted from its bearings by a crane and the coil slipped off the smaller end, and lauded on end on an iron plate, in order that it may cool without bulging or warping. The coil in this condition is about 50" or 60" long and loses about .2 of its length in the subsequent welding and turning, the finished coils averaging about 36" in length. After coiling, the cross section of the bar is slightly concave on the exterior and convex on the interior of the coil, while the distances between the folds are less on the interior than on the exterior. When removed from the shaft the folds are very open, and the ends of the bar project out from the coil. The ends are heated and hammered down to conform to the shape of the coil.
The coil to be welded is placed on the end of a long porter bar, having a movable balance weight at the other end, and laid horizontally in a reverbatory furnace so that the flame may entirely surround it, and, as nearly as possible, heat all parts alike. When the coil arrives at a red heat it is taken out of the furnace on the porter bar, and shoved into an iron pipe which is canted on one side to receive it. This pipe is made of cast iron 4" thick, 4' long, and 14" interior diameter. The pipe with the coil inside is then placed directly under an eight ton steam hammer, and given a few light blows to force the coil firmly together along the surface of the bore. It is then removed from the pipe, replaced in the furnace and when raised to a welding heat again put in the pipe, a die placed on top and set under the steam hammer, when it receives seven or eight heavy welding blows. The coil is then returned to the furnace and the same process gone through with a second time, after which it is allowed to cool. This coil welding is considered the most important part of the whole conversion, as any impurities lodging between the folds of the coil before they are closed, or too great a loss of welding heat between the furnace and the hammer will prevent a perfect welding of the iron. In order to avoid weak or imperfect welding of the folds, it is desirable that the process should commence at the interior surface of the coil and progress gradually outwards, thus leaving to the last an open joint on the exterior for the escape of cinder squeezed out during the operation. This end it is thought is secured by the particular form of cross section given to the bar, and by the precaution taken of first closing the folds of the coil along the interior surface. The use of the pipe for coil welding, by means of which the coil is prevented from bulging to any great extent or losing much heat, is different from the method pursued in England and thought to be superior to it.
The welded coils when cool are bored out sufficiently to detect any flaws, and their ends faced and reciprocally recessed for uniting. The projection or shoulder is slightly longer than the depth of the recess, so that when the coils are pressed together in the furnace the first welding will take place in the interior. The recess is also slightly smaller than the shoulder, and is expanded and shrunk over it, thus holding the two coils together while being placed in the furnace. The furnace for welding the coils is 5' long by 18" wide, and in the centre of each side is a door through which the coil is introduced, and out of which the ends project. The fire is underneath and the flame made to entirely encircle the joint before passing up the stack, so as to heat all parts as equally as possible. On each side of this furnace is a cross head; one being fitted with a broad bearing plate for one end of one coil, and the other with a large screw for the opposite end of the other coil. This screw is turned by means of a long spoked wheel capable of exerting a pressure of one hundred tons. By means of keys, and slots in the rods connecting the cross heads, the latter can be secured at any required distance so as to accommodate any length of coil. As the joint arrives at a welding heat the press is screwed up, and the coils driven into each other. The two coils thus united form a section, and two sections similarly united form a tube. When judged to be perfectly welded, the section is withdrawn from the furnace, and the bulging straightened under the hammer. After the two sections have been united and straightened, the tube is bored out to within 1-10 of its final diameter (to 7."2) and a cut taken off the outside. It is then carefully inspected and subjected to a water pressure of one hundred and forty pounds to the square inch. After inspection the tube is put in the turning lathe and turned down at the breech end for a distance of 32" to an exterior diameter of 10" and the end of the cut rounded up to the outside of the tube. Around this reduced portion a spiral groove or gas escape is cut 0."05 deep and 0."1 wide with a pitch of 8," thus making four complete turns round the end of the A tube.
The B tube, which is shrunk on the reduced portion of the A tube, 32."75 long, 1."75 thick, and the inner edge of its front end rounded to fit the A tube. It is made in one coil in the manner already described, wound in the same direction, and shrunk on with a shrinkage of 0."003 in the diameter. The B tube besides strengthening the system is a safeguard against the bursting of the gun. If the A tube is ruptured, the gas issuing from the gas escape gives timely warning of the damage done before the B tube and the cast-iron casing give way. The B tube in order to be shrunk on, has to be bored to that degree of smoothness which is necessary for close contact, and is gauged to 0."001 every few inches of its length; to these measurements the shrinkage is added and a plan made out by which to turn down the exterior of the A tube in order that it may exceed in diameter the inside of the B tube by the amount of shrinkage desired.
When it is necessary to make one tube fit over another, the inside of the exterior tube is always turned first to as near the required dimensions as possible, and the exterior of the other tube turned to fit it, for the reason that more accurate turning can be done on an exterior than on an interior surface.
The operation of shrinking on the B tube is comparatively easy and the heat required not very great. Wrought iron, on being heated from 62° F to 212° F (or through 150° F), expands lineally about 1/1000 of its length; therefore to obtain sufficient expansion to allow the B tube to pass over the A tube it is not necessary to heat the iron to more than 600° F or to a point where it has not lost its blackish hue and attained the red, which it does at 575° F. This leaves a wide margin for error as no harm is done by over-heating provided the temperature does not rise to the point where scale forms. In order that the shrinking may not be retarded by the expansion of the inner tube, it is kept cool by a stream of water on the inside. After the B tube is shrunk in place the breech end of the tube is closed with a forged wrought iron screw cup, which forms the bottom of the bore. This cup is 5."5 long, 8" in diameter across the threads and recessed on the front face to a depth of 2."5. The thread in the end of the A tube is raised above the surface of the powder chamber so that there may be no weakening by cutting away the metal unnecessarily. After-the cup is screwed into place the tube is again subjected to a water pressure of one hundred and forty pounds to the square inch.
The tube is nest placed in the rifling machine and rifled to the following dimensions:
Twist uniform, one turn in 40 feet (60 calibers).
15 lauds and grooves, each 0." 83776 wide.
Grooves 0." 075 deep.
The rifling commences at 10", from the bottom of the bore.
After rifling, the tube is fine turned to fit the casing. The dimensions of the finished tube are as follows:
Length of bore 128." 2 (16 calibers).
Diameter of bore across lands 8."
External diameter 13.''5.
The outside corner at the breech end is rounded with a radius of 1"75. This is a longer radius than that of the corresponding curve in the cast iron (1."7), in order that there may be no wedging action and a tendency to split open the casing when the tube is set out by repeated firing. The exterior of the muzzle end is reduced to 2" in thickness for a distance of 3".75 to admit the muzzle ring.
In point of fact the tube is a very little less in exterior diameter than given above, a play of not more than 0."007 at the breech end to about half way to the muzzle, and not more than 0."015 from there to the end being allowed. All this play is taken up in firing, and after that the tube calls directly upon the walls of the gun for support. The bore of the cast iron casing is measured with the star gauge at certain points and the outside of the tube with accurately prepared horseshoe gauges.
The next operation is the placing of the tube in the gun. On account of the play allowed the tube slides in quite easily, a small threefold purchase being used to force it home. As perfect contact at the bottom of the bore is essential, the end of the tube is smeared with red lead, and then shoved home. On withdrawing it the prominent points are shown by the absence of the red lead and are filed down. This is repeated several times till the equal distribution of the lead on the end of the tube shows that it bears evenly against the cast iron. To prevent any working forward of the tube owing to the compression of the metal during repeated firing, it is confined by the muzzle-ring. This ring is made of composition, 3".75 wide, 12" interior diameter, 1." thick, with a rounded thread on its exterior to correspond with the thread already mentioned as cut in the cast iron. To prevent the tube from turning in the casing, a steel steadying plug 1."5 diameter is screwed through the cast iron and 0."75 into the tube at about 17" in front of the right rim-base.
The gun is next vented. A vertical hole 1" in diameter is bored through the end tube, 2."5 to the right of the axis of the bore and 3."5 from the bottom of the bore. In this hole is screwed the copper boushing, which ends in a hexagonal nut or shoulder on the outside of the gun. Properly speaking the gun has no chamber, the unrifled portion having the same diameter as across the lands.
The guns when finished, are subjected to a proof often rounds; five rounds with twenty pounds of hexagonal powder, and five with thirty five pounds: the shot in each case weighing one hundred and eighty pounds. The average enlargement of the tube at a point 118" from the muzzle or about the centre of the cartridge is 0."02, the play being deducted. The enlargement in the powder chamber gradually diminishes towards the muzzle and at a distance of 68" from it, no appreciable expansion can be found. Where the expanding ring on the shot takes the grooves the enlargement suddenly increases for two or three inches and then as suddenly decreases; this occurs at 28." from the bottom of the bore. As the thirty-five pound cartridge occupies but 24" from the bottom, and as the shot when home is placed close against it, the shot has evidently a forward motion of 4" before the ring fully takes the grooves. When the charge is ignited a comparatively small pressure is required to start the projectile from its seat, while a much greater pressure is required to expand the ring. When this expansion occurs, the windage being suddenly reduced and the shot in a slight degree retarded by the friction of the ring, an opportunity is given for the formation of a much larger amount of gas, which delivers a blow on the tube and shot. The latter being forced forward by this blow more rapidly than before, relieves the strain on the tube almost as suddenly as it was formed, but at the same time it leaves the tube slightly enlarged at this point.
The velocities obtained during proof, with Benton's Thread Velocimeter, were as follows; viz.
Charge of powder
Number of fires
Average initial velocity
The velocities were taken at a distance of 175' from the muzzle of the gun and with 1° depression.
The following is the average internal pressure, viz.
Charge of powder
Number of fires
Average internal pressure
20746 lbs. per square inch
30080 lbs. per square inch
No flaws or imperfections of any kind were developed during proof.
Before deciding on the present method of conversion, an Army Ordnance board carried out a series of experiments to determine whether steel or iron would be the proper material of which to form the lining. Four ten inch Rodman smooth bores were converted two into 8" rifles and the other two into 9" rifles, one of each caliber with a wrought-iron, and the others with a steel tube. The wrought-iron tubes were inserted as has already been described for the Navy gun. The steel tubes were 2" in thickness, reinforced on the breech end to a short distance in front of the trunnions by a steel jacket 2" thick, shrunk on, and still further supported in the rear by a steel screw plug through the jacket. The whole was inserted from the breech end and held in place by a coarse screw thread on the jacket which worked in a corresponding thread in the cast-iron. The only difference in the manufacture of the 8" and 9" steel lined guns, was that in the 9" gun the cast-iron casing was expanded when the tube was screwed in and then allowed to shrink on it. The wrought-iron tubes were made at Sir William Armstrong's works at Newcastle-upon-Tyne, England; and the steel tubes and jackets were manufactured by the Bochum Manufacturing Company, Bochum, Prussia.
No. 1, 8." wrought iron tube, has fired, up to the last reports published, seven hundred and sixty-one rounds; some small weld marks are noticeable in the bore, but the gun is still considered as serviceable as it was in the beginning.
No. 2, 8." steel tube. At the one hundred and seventy-first round, a small crack was noticeable, which increased as the firing progressed; at the four hundred and fifty-sixth round, or two hundred and eighty-five fires after the tube split, the gun blew to pieces.
No. 3, 9." wrought iron tube, has been fired five hundred and two rounds in all, and is still in perfect condition.
No. 4, 9." steel lined, no reports.
No. 5, 8" wrought iron tube, manufactured by Paulding Kemble and Co., Cold Spring N. Y., has been fired five hundred rounds, and shows less erosion of the bore than either No. 1 or No. 3 experimental guns, for the same number of rounds.
During the proof of the Navy guns, the average internal pressure, using thirty-five pounds hexagonal powder, the battering charge, was thirty thousand pounds per square inch. This at the surface of the cast iron bore, would only give, at the very greatest, a pressure of eleven thousand pounds per square inch or a strain a little over one third of the tensile strength of the cast-iron. It is evident from these figures and from the tests for endurance to which the experimental guns were subjected, that this system of conversion is a very strong one; also that wrought iron is a more reliable material than steel for the tube. The Army experiment have fully proved that American coiled tubes are fully equal if not superior to the English coiled tubes.
More work has been obtained from the Navy 8." rifle, than from the English 8.9" ton gun, or the Army 8' rifle, firing the same charge of powder and the same weight of projectile. This is probably due to its greater length of bore.
Navy 8" rifle, caliber to length of bore, 16 to 1. I.V. 1466.7 ft.
Army 8" rifle, caliber to length of bore, 14.6 to 1 I.V. 1374.0 ft.
English 8" rifle, caliber to length of bore, 14.7 to 1 I.V. 1413.0 ft.
The projectiles for the 8" rifle are of two kinds; a cored, cast-iron, chilled head shot of one hundred and eighty pounds; and a long cast iron shell of one hundred and eighty pounds. The points are ogival, struck with a radius of 1 ¾ calibers. The rifle motion is imparted by means of an expansion ring. This ring—the invention of Capt. Butler, U.S.A.—is double-lipped, and either screwed or cast on a reduced portion at the base of the shot. When the charge is ignited the gas enters the annular groove between the lips, expands the outer lip uniformly all around into the rifling, while at the same time the inner lip is made to grip the shot more closely; thus insuring its receiving the proper twist and effectually preventing stripping. This expansion centers the base of the shot. The ring is purposely made sufficiently stiff so as not entirely to fill the grooves and cut off all windage. The forward end of the projectile is centered by the pressure of the gas escaping through the grooves surrounding and supporting the shot during its passage along the bore.