This large number of pieces necessarily renders the operation of securing perfect welding much more difficult, and the liability of loss is greater. Some imagine that the curly figures of the barrel are simply etched on the outside, when they are, in fact, the visible proof of a superior strength both desirable and important to every shooter who cares for his personal safety; for if an iron barrel, no matter how strong and thick, is defective and does not stand the test, the defective part will splinter into more or less small pieces, while the Damascus, Bernard, and laminated barrels will tear like a woven fabric. This proves clearly the extraordinary tenacity of the material. These fine bar rels are not, therefore, worked and twisted so neatly and nicely that they may look beautiful alone, but rather for the reason that greatest lightness, com bined with greatest durability, may be produced.
Each barrel, after manufacture, should be carefully tested, and submitted to the necessary praof. The diameter of the bore should be verified with the standard and limit gauges. The standard gauge is a cylinder of the diameter of th.e bore, and the limit gauge is .0025 inch greater, The former should pass freely through the bore, and the latter should not enter it. The barrel shoula enter the groove of the stocic one-half of its diameter, and it should bear uniformly throughout, particularly at the breech. The vent should be accu rate in its dimension, position and direction, and a wire should be passed through it to see that it is free. The cone should be sound. The shoulders of the breech-screw should fit closely to the end of the barrel, and it should be free from cracks or flaws about the tang-screw hole. The straightness of the barrel may be ascertained by turning out the breech-screw, and holding the barrel up to the light, and reflecting the image of a straight-edge from the surface of the bore. If the barrel be straight, the reflected image will be straight in all positions of the barrel. The bore must be free from all hammer marks, ring,-bores, cinder-holes, flaws, cracks, etc., as such irregularities cause an inaccuracy of fire.
A wrought-iron rifle or carbine barrel will only endure about one half of this charge. The breech-loading system after it is finished and assembled to the barrel is subjected to a "finished-proof- charge of a single service bullet and a charge of 85 ,grains of musket-powder, which is all that can be crowded into the cartridge-shell. Numerous trials have shown that the Springfield system will stand at least 120 grains of powder and three service bullets, weighing altogether 1,265 grains. The fact that a small-arm barrel
seldom or never bursts or swells at the muzzle in proof shows conclusively' that when such defects are found in service the cause is some obstruction in the bore. Obstructions arise generally from the improper stopping up of the muzzle to keep out moisture. It may arise from dirt introduced by resting the muzzle of the piece on the ground. Instances have occurred of the bursting of barrels by a bullet in the bore—the result of a charg,e insufficient to expel it. Very accurate and delicate machines are now used to weigh each finished cartridge, and reject any that may be deficient in powder. The barrel of a rifle will endure at least io,000 fires helot': its accuracy is sensibly impaired: and its exterior dimensions may be very much reduced by wear without impairing its strength for service.
In the manufacture of rifle barrels the finest machinery is now used. The advent of the barrel-drilling machine has affected the manufacture of the smaller caliber rifle barrels to a greater extent than any other invention of the past fifty years. The operator can. without any particular effort of me chanical skill, drill a continuous hole through solid stock. with little deviation from a straight central bore of uniform size, if conditions are what they should be.
I No particular apparatus is required for starting the drill: neither is any ' straightening required during the operation, and little or none until after the i proof reaming.
The machine is double and has a horizontal bed. The heads are at the I , end and have mounted in them independent spindles parallel to each other. ! On their inner ends are chucks for securing and rotating the barrels in the adjustable rests which support, guide and control the starting of the drills, which are secured in the sliding carriages. These are fed positively 38 inches by a screw having automatic stops. The screw has a variety of speeds through change gearing, to compensate for different qualities of stock to be drilled.
Two rotary pumps (one for each barrel) force oil, supplied from a tank placed underneath the machine, through a series of tubes into and through the drill. The oil lubricates the cutting lip, and forces out the chips into the basin on top of the tank, where they are drained, and the strained oil returned to the pump again.