CHAPTER XXIV. ON NIPPLES OR CONES. The terms nipple, cone and tube are applied in rather an indiscriminate manner to that portion of a gun breech on which the copper cap containing the fulminate designed for firing the arm is placed. To be good and serviceable, the nipple should be made of steel, and carefully tempered; but many are made of a low grade of steel, of common iron, and even malleable iron has been used, and case-hardened to render them fit for use. [Illustration: FIGURE 50.] [Illustration: FIGURE 51.] [Illustration: FIGURE 52.] _Forms of Nipples._—There are as many forms of nipples as there are qualities, and they may be divided into classes, as the musket nipple (called “cone” by the armory operatives), the American, English, and German. The German have coarser threads than the American. The English musket nipple has a thread or screw of 18 threads per inch; it has a flat top, and has a hole of one taper, being large at the bottom and smaller at the top. The American musket tube has a screw of 24 threads to the inch, has a vent resembling two inverted cones, meeting with a small opening near the centre. The top of the nipple, consequently, resembles a narrow circular ring. Fig. 50 shows the English nipple, and Fig. 51 the American; Fig. 52 the different forms of vents. _Nipples for Breech-loading Arms._—For breech-loading arms, using loose powder and ball, the nipple is made similar to the American, but the vent is made quite large at the top, and decreases like an inverted cone, and terminates in a small opening a little larger than a common pin. In this nipple the fire from the cap is concentrated and caused to rush with some force through the small aperture, the same as heat is concentrated in a single point by using a blow-pipe for that purpose. The object is to burn through the material of which the cartridge is composed. _Nipples with Flat Tops._—The use of a nipple with a broad, flat top requires a vigorous mainspring, and then quite a volume of the detonating flame escapes outside the nipple and between it and the cap. The small portion that passes down the tube may be so impeded, if the nipple be foul or rusty, as to cause the gun to hang fire, and even to miss fire. Should the mainspring be too weak, the cap will come in contact with the broad surface of the nipple, forcing the priming of the cap from its position, and leaving it unexploded. Often the cap is made to bear the blame, when the fault is due entirely to the formation of the top of the nipple.