In the United States the perfection to which muzzle-loading smooth-bores had been brought blinded the people to the value of the rifle. Many Parrott rifles were made and used in the navy, but it was never a favorite gun. After the close of the Civil War the development of ordnance in calibre of 13 inches and wrought-iron cores in serted, and these were in turn bored out to a diameter of 8 inches and rifled. In the develop ment of the new ordnance (1880-85) all sorts of difficulties were met, the chief of which was the crop of ideas which the mistaken views of the preceding twenty years had fostered. The Dahl gren and Rodman smooth-bore guns had become an article of faith with the American people, who had been taught to believe that their naval suc cesses were due to cast-iron smooth-bore guns, instead—which was the being won in spite of them. Numerous inventors and manu facturers appeared before Congress with ideas based upon our previous mistaken practices, but the breech-loading, forged-steel, built-up gun con- • quered its way past all attempts to supplant it. The slotted-screw breech-block was used in all the new guns. The design of these pieces was prac tically the same as that of the best foreign practice, and included a tube extending the full length of the' bore; a heavy jacket in one piece extending from the breech end of the tube for a little more than half its length; over the jacket a row of hoops; and over the tube beyond the both army and navy ceased—largely owing to lack of funds, Congress refusing to grant money for new work. All sorts of repairs and make shifts were resorted to, such as cutting off the breech of Parrott rifles, putting on a larger hoop, jacket, hoops extending part way or all of the way to the muzzle. The first guns were made of 30 calibres length; between 1883 and 1890 the length increased to 35, after 1890 to 40 and 45 calibres, until the last model, that of 1899, inserting a lining tube, and making them into breech-loaders. ( See ORDNANCE.) Eleven-inch Dahlgren smooth-bores were reamed out to a brought out guns of 50 calibres in the sizes below the 7-inch.
The breech mechanisms used in the United States naval service are the Fletcher (several modifications), Dashiell, Vickers-Maxim, Hotch kiss, and Driggs-Schroeder. The Fletcher, which is a development of the Farcot system, is prob ably the simplest, and is certainly one of the neatest and strongest breech mechanisms known. A worm-wheel on a vertical spindle works in a rack on the breech-plug, and first causes it to turn and disengage the threads and then move to the rear and turn out clear of the breech. The vertical spindle is driven by a worm and worm wheel in the larger calibres, in the smaller ones simply by a handle pivoting on it. The Dashiell and Vickers-Maxim are operated by a short arm driven from the vertical axis of the operating lever, which shifts its centre during the motion. The Hotchkiss breech-block is a vertically sliding wedge, and the Driggs-Schroeder block drops to clear its upper end from the housing of the breech and then revolves to the rear about a horizontal axis; these two mechanisms are only used in 6 pounders and smaller pieces. See RAPID-FIRE
Guics.
while the next is another blank from which the succeeding sectors rise in steps, as from the first one. The advantage of the \Velin system is that three-fourths or five-sixths (if desired) of the circumference of the block is available for screw All new guns in the United States Navy are fitted with the Welin system of breech-closure, a modification of the slotted screw. The inside of the screw-box is cut !May in steps in the fol lowing manner: It is divided by twelve (usual number) radial planes; three of the sectors are smoothed out to a maximum diameter, and form the blanks of the screw-box; the next sector (in the direction toward which the block turns in closing) has a radius which is less by a little more than the height of the threads on the block or in the screw-box; the next has a radius smaller than the preceding by a similar amount; the next sector is likewise reduced in radius; surface to resist the powder pressure instead of one-half as in the old block of ordinary model; this enables the \Velin block to be made shorter, and therefore lighter.
The gas-checks used in naval guns are the Broadwell ring or cup gas-check used by Krupp, and some modification of the De flange gas-check, such as is used in United States naval ordnance and in nearly all ordnance using a screw breech block. The Broadwell ring is a steel ring with a section somewhat like a letter L. When the gun is fired the pressure of the powder gas presses the lips of the ring against the walls of the chamber and against the face of the breech-block, and so cuts off the escape of the gas to the rear. The De flange gas-check is more complicated. As originally made, it consisted of a ring-shaped pad of asbestos saturated with suet, covered with canvas, and held between two disks with large holes through their centres, through which, and the hole in the pad, passes the stalk of the steel block called the mushroom, because of its shape. The disks holding the pad between them are themselves held between the mushroom head and front face of the breech-plug. The opposing faces of the disks are hollowed out so that a section of one side is somewhat like half of the letter I. When the powder pressure acts on the mushroom head the pad is squeezed and forced out against the surface of the bore, and at the same time the outer lips of the disks are also forced outward against it; this combination of metallic and pad contacts cuts off all escape of gas to the rear. In the latest types of gas-checks used in United States naval guns the shape of mushroom head, gas-check, and rings has been modified, but the principle remains the same. The front disk (and in some cases the other as well) is now usually split on one side by a plane passing through the centre of the disk and making an angle of about 75 degrees with the axis of the bore; this per mits of a close fit without danger of jamming or sticking. In guns using fixed ammunition the cartridge-case acts as a gas-check, its thin walls expanding under the action of the powder gas until they press against the walls of the chamber so tightly that no gas escapes.