R0IMAN CAST-IRON GUNS. A casting cools and solidifies first on the surface, then pro gressively inward. The metal contracting as it solidifies draws inward from the solid outer shell, and the inner portion is thus put muter tensile strain, while the outer is compressed by the reduction of its diameter. The effect of powder pressure in the bore is to strain the inner portion by tension. If now' this inner shell be already under tensile strain, it is pre disposed to rupture. General Rodman, Ordnanee Department, United States Army, 'announced this condition, and proposed to avoid it by casting guns hollow and eooling them by water from the interior of the bore, while the exterior was kept hot by fire; the bore-surfaee then solidify ing first would he compressed by the contraction of the outer layers, which would consequently be under tensile strain. The gun would there fore be stronger than a gun cast solid and cooled from the exterior, or even one without initial strain. Rodman's system of construction, used in Ameriea and elsewhere for many years, gave the best results possible with east iron. and was superseded only when the demand for rifles and higher power necessitated the use of stronger material. See ARTILLERY for illustration of Rodman gun.
Chambers (United States) patented in 1849 a gun of wrought-iron tube with strengthening hoops. In 1S55 Blakely (England) and Tread well (United States) invented guns with hoops shrunk on. To them is due the real origination of the built-up system. Sir W. G. Arnistrmig (q.v.) of England made built-up guns for the ing and forced on by hydraulic pressure. The \Vest Point Foundry (Parrott's) at Cold spring, N. Y., to meet the demand for a cheap and quickly made rifle for use in the Civil War. made hollow cast-iron guns reinforced by a band of coiled wrought iron shrunk around the breech. These were the well-known 100-. 200-, and 300 pounder Parrott rifles, and served their purpose admirably, but the system was not capable of extension. Cast iron was, as always, unreliable.
The adoption of rifled guns. commencing about 1560, found all nations with large stocks of east-iron smoothbores on their hands. Parsons United States) in 1560 planned to convert these to rifles by inserting a steel tube through the breech and then ()losing that end by a permanent screw plug. Sir W. Pallier (England) in l 63 suggested a tube of coiled wrought iron inserted from the muzzle end of the gun. In the Palliser system the tube was prevented from forward motion by a collar screwed in front of it into the cast iron. Forward motion of Parsons's tube was prevented by several shoulders. This was the better as the tube was thus sup ported at several points with iess danger of opening the welds between the coils. The Pal liser systein, which was cheaper, was adopted in England, and many guns converted by it. In America, between 1S74 and 18SO. many 10-inch guns were so converted into S-inch rifles, com paring favorably with contemporaneous European rifles. Experiments were made in the of larger calibre guns, in some of which the welds gave trouble, causing general distrust of muzzle-insertion, and the last A-inch converted rifles had breech-inserted Variation: of this conversion system were proposed for original construetion, and several such gun: were built and tested, notably the 12.25-ineh rifle, between 1870 and 1850. Cast-iron bodies hooped with English service from 1S5S. For many years his hoops were formed by coiling a rectangular bar of iron helically about a mandrel, and then closing and welding the coils together. Thee hoops were shrunk on the tube with initial tension. Whitworth were built up of east and forged homogeneous steel hoops without shrinkage, the hoops being made slightly taper steel were strongly advocated by some. and the United States model 1886, 12-inch breeeh-loading mortars, made in this way, are now in service.