GUNS. 381 GUNS. States naval service me the Fletcher (several modifications) , Dashiell. Viokers-Maxim, lUiloh- Uiss. and Driy:i;s-ScluiHHk'i-. The Fletcher, which is a development of the Farcot system, is ])rob-
- ibly 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 liandle pivoting on it. The Dashiell and Vickers-Maxim are operated by a sliort 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-Sehroeder 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 GUN.S. Breech open. VICKER8 BREECH .MECHANISM. SHOWING WEI.IN BREECH. All new gims in the United States Xavy are fitted with the Wei in system of breech-closure, a modification of the slotted screw. The inside of the screw-bo.x is cut away 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 bfanks of the screw-box; the next sector (in the direction toward which the block turns in closing) has a radiiis which is less by a little more than the height of the threads on the block or in the serew-hnx : the next has a radius smaller than the preceding by a similar amount; the next sector is likewise reduced in radius; while the next is another blank from which the succeeding sectors rise in steps, as from the first one. The advantage of the W'elin system is that three-fourtlis or live-sixths (if desired) of the circumference of the block is available for screw- UNITED STATES NAVAL BREECH MECHANISM FOR .MARE HI. 1'2-INCH GUNS. SHOWING DE HANGE GAS-CHECK. .4, mushroom head : B. mushrooiu stem ; C, breech-pluj^ ; D, frictionless washer; EE, lock nuts : F, operating crank. surface to resist the powder pressure instead of one-half as in the old block of ordinary model; this enables the Wei in block to be made shorter, and therefore lighter. The gas-checks used in naval guns are the Broadwell ring or euj) gas-check used by Krupp, and some modification of the De Bange 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 again.st the face of the breechbloek, and so cuts off the escape of the gas to the rear. Tlie He Barige 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 wliieh, 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 Iheiiiselves held between the mushroom head and front face of the brecch-plug. The opposing faces
