8-Inch "180-Pounder" Muzzle Loading Rifle manufactured from an 11-Inch Dahlgren Shell Gun on display at Patriot's Point Soccer Stadium near Charleston, South Carolina.

The 1880 edition of A Text Book of Naval Ordnance and Gunnery Prepared for the Use of Cadet Midshipmen of the United States Naval Academy written by Augustus Paul Cooke contains a detailed description of the manufacture of 8-Inch, 8-Ton, 180-Pounder Muzzle Loading Rifles from 11-Inch Dahlgren Muzzle Loading Smoothbore Shell Guns.

My original post on the four 8-Inch Muzzle Loading Rifles Preserved at Patriots Point is here: https://www.santee1821.net/preserved-artillery/8inch-dahlgren-rifles-at-patriots-point

The digitized copy of Cooke’s book may be found on Google Books here: https://books.google.com/books?id=vTZ92PqoNlgC

The text and images below are taken from the 1880 edition of Cooke’s textbook, pages 232-235.

The Manufacture of the 8-Inch, 8-Ton, 180-Pounder Muzzle Loading Rifle

8-Inch Muzzle Loading Rifle cutaway illustration — Illustrations on page 80 of *A Text Book of Naval Ordnance and Gunnery Prepared for the Use of Cadet Midshipmen of the United States Naval Academy* showing the 8-Inch Muzzle Loading Rifle

637. 8- INCH M. L. R. -This gun is built up by lining an XI-inch M. L. S. B. gun with a jacketed tube, combining in its construction the principles of Initial Tension and Varying Elasticity. (Fig. 111.)

638. MANUFACTURE OF THE TUBES. - The operation of making a tube is divided into three parts, rolling, coil-welding and tube-welding.

639. Rolling.-The bar to be rolled into a coil is 36 feet long, 3½ inches thick, and of tapering width, being 4 inches on the outside, and 34 inches on the inside ; it is placed in a long furnace, and heated by a blast to a good red heat; it is then drawn out and rolled around a shaft 6½ inches in diameter, and slightly tapering at one end. The shaft with the coil upon it is then lifted by a crane from its bearings, and the coil slipped off the tapering end ; it is received upon a flat iron plate, where it is allowed to cool without losing its alignment.

640. Coil-welding.-The coil to be welded is placed on the end of a long porter-bar, having a movable balance- weight on the other end, and laid horizontally in a reverberatory furnace. When the coil arrives at a red heat it is taken out of the furnace on the porter-bar and placed in a cast-iron cylinder called a welding-pot, in which it is then drawn vertically under an eight-ton steam-hammer, and given a few light blows to force the coil firmly together ; it is then replaced in the furnace, and when raised to a welding- heat is again placed in the welding-pot under the hammer, and receives seven or eight heavy welding-blows ; this welding-process is repeated, after which the coil is allowed to cool. This process is considered the most important of the whole operation, 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 pre- vent a perfect welding of the coil.

641. Tube-welding.-The welded coils are first bored out sufficiently to detect any flaws, and their ends faced and reciprocally recessed for shrinking together. 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 expanded and shrunk over the shoulder, thus holding the two coils together while being placed in the furnace. The joint is then placed in a reverberatory furnace 18 inches wide and 5 feet long, having in the centre a door on each side through which the ends of the coils project, and the blast falls only on the joint. A cross-head, sup- ported by two iron bars, is placed against one of the projecting ends, while a screw-press of one hundred tons is brought to bear on the other end. As the joint arrives at a welding-heat, the press is screwed up and the coils driven into each other.

642. The A Tube. -Two coils united form a section, and two sections similarly united form a tube. When judged sufficiently united, the section is withdrawn from the furnace and the bulging around the joint straightened under the hammer. The welded tube is then bored out to within one-tenth of its final diameter, and a cut is taken off the outside. It is then carefully inspected and subjected to a water- pressure of 140 pounds. After inspection the tube is put in the turning-lathe, and turned down at the breech to receive the B tube.

643. The B Tube. -The B tube is made from a welded wrought-iron coil, constructed in the manner already described, 32 inches long and 1.70 inches thick ; it is shrunk over the breech-end of the main or A tube, with a shrink- age of 0.003 of an inch, the A tube having previously been turned down 1.75 inches to receive it. Around this reduced portion of the A tube a spiral groove or gas- escape, 0.05 of an inch deep and 0.1 of an inch wide, is cut, which communicates with a small hole bored through the breech when the tube is in position in the gun. This arrangement of the B tube and gas- escape is a safety measure, the intention being that any fracture of the A tube underneath the B tube, sufficient to allow the escape of gas into the groove, will immediately be indicated at the breech of the gun, and give timely warning of the danger with- in. A screw-plug, 5.5 inches, closes the breech-end of the tube, and forms the bottom of the bore. The plug is screwed into a plus thread on the A tube so as not to diminish its strength, and the face of the plug forming the bottom of the bore is chambered to assist in preventing the escape of gas. The tube is then rifled and turned to fit the bore.

644. The Conversion (Fig. 111). -An XI-inch gun is bored out to a diameter of 13.5 inches, and a thread cut at the muzzle for the muzzle-ring. The jacketed tube is accurately fitted to the cast-iron casing, allowing a variation of only .007 of an inch at the breech and .005 of an inch at the muzzle : the tube being placed in the casing is secured in position by the muzzle-ring screwed in the muzzle between the tube and the casing. (Fig.112.) A small pin or steadying plug is screwed through the casing and into the tube on the side just forward of the trunnions to prevent the tube from turning. As the preponderance of the guns was changed after conversion from plus to minus at the base-ring, the axis of the trunnions is carried forward 1.5 inches by first turning them down eccentrically and then fitting on a composition-sleeve. The present preponderance is plus 300 pounds at the base-ring, and the weight of the converted gun is 17,330 pounds. As these guns are to be fired with friction-primers, the lock-masses have been re- moved. The vent-piece, which is of copper, 1 inch in diameter, is screwed in through the casing and tube, and has a nut and shoulder on the upper end.