_U. S. Rifling Machines._—The rifling machines in use by the U. S. Government at the Springfield Armory for cutting their grooved rifles may thus be described: The barrel is placed in a horizontal position in an iron frame, and held there very firmly. The grooves are made by three short steel cutters placed within three mortices, made to receive them, near the end of a steel tube which is moved through the bore of the barrel by slow rotary and progressive motion. The cutters are narrow pieces of steel having upon one side three angular shaped teeth about one-sixteenth of an inch in height, and of the width of the groove, ground to a very sharp edge at the top. It is these which produce the rifling. The three cutters, when inserted in the tube, form upon their inner surface a small opening which decreases toward the inner end. Into this is inserted a tapered steel rod, and is so controlled by a connecting cog-wheel that this rod is pushed, at every revolution, a little further into the tapered opening formed by the inner edges of the three cutters. The effect of this is to increase the pressure of the cutters upon the inner surface of the barrel, and thus gradually, at each stroke of the machine, deepen the cuts as produced by the rifling. The rod makes about twelve revolutions in a minute and it occupies about thirty minutes to rifle a barrel. [Illustration: FIGURE 42.] _Old-Fashioned Rifling Machine._—But the gun-maker who builds rifles to order, and perhaps then but a single one at a time, uses quite a different apparatus for rifling, although the principle involved is the very same. Many of the old gunsmiths made their own rifling machines. The simplest form was a common joist, two inches thick and six inches wide. The length about twice that of any barrel to be rifled. At one end, on the narrow side, was fixed in two bearings, one at each end so as to turn freely, an old rifle barrel. At the other end of the timber, in a line with the barrel was fixed two standards in which to firmly fasten the barrel to be rifled. At the end of the old rifle barrel, and on the end nearest to the end of the timber was fixed a circular plate of iron, like a wheel which was made with divisions on its circumference, and had a catch which was fastened to the wood, and when the end of this catch engaged one of the divisions it would firmly hold the barrel in place. When this plate was turned the barrel also turned. Inside of this barrel was placed a rod of iron, around which was cast some soft metal, as babbit metal or old type metal, or even lead. This was done by putting the rod in the barrel and then pouring in the metal when melted. A handle, similar to an auger handle was fixed transversely to one end, but in such a manner as to turn around freely on the rod. As the rod was pushed back and forth the soft metal followed the rifling grooves, and this caused a turn, first in one direction and then in another. By the