Artillery Through the Ages | Page 8

good results was the cast-iron 4-1/2-inch siege gun. This piece was cast solid, then bored, turned, and rifled. Uncertainty of strength, a characteristic of cast iron, caused its later abandonment.
[Illustration: Figure 13--PARROTT 10-POUNDER RIFLE (1864).]
The United States rifle that was most effective in siege work was the invention of Robert P. Parrott. His cast-iron guns (fig. 13), many of which are seen today in the battlefield parks, are easily recognized by the heavy wrought-iron jacket reinforcing the breech. The jacket was made by coiling a bar over the mandrel in a spiral, then hammering the coils into a welded cylinder. The cylinder was bored and shrunk on the gun. Parrotts were founded in 10-, 20-, 30-, 60-, 100-, 200-, and 300-pounder calibers, one foundry making 1,700 of them during the Civil War.
All nations, of course, had large stocks of smoothbores on hand, and various methods were devised to make rifles out of them. The U. S. Ordnance Board, for instance, believed the conversion simply involved cutting grooves in the bore, right at the forts or arsenals where the guns were. In 1860, half of the United States artillery was scheduled for conversion. As a result, a number of old smoothbores were rebored to fire rifle projectiles of the various patents which preceded the modern copper rotating band (fig. 12c, d, f). Under the James patent (fig. 12c) the weight of metal thrown by a cannon was virtually doubled; converted 24-, 32- and 42-pounders fired elongated shot classed respectively as 48-, 64-, and 84-pound projectiles. After the siege of Fort Pulaski, Federal Gen. Q. A. Gillmore praised the 84-pounder and declared "no better piece for breaching can be desired," but experience soon proved the heavier projectiles caused increased pressures which converted guns could not withstand for long.
The early United States rifles had a muzzle velocity about the same as the smoothbore, but whereas the round shot of the smoothbore lost speed so rapidly that at 2,000 yards its striking velocity was only about a third of the muzzle velocity, the more streamlined rifle projectile lost speed very slowly. But the rifle had to be served more carefully than the smoothbore. Rifling grooves were cleaned with a moist sponge, and sometimes oiled with another sponge. Lead-coated projectiles like the James, which tended to foul the grooves of the piece, made it necessary to scrape the rifle grooves after every half dozen shots, although guns using brass-banded projectiles did not require the extra operation. With all muzzle-loading rifles, the projectile had to be pushed close home to the powder charge; otherwise, the blast would not fully expand its rotating band, the projectile would not take the grooves, and would "tumble" after leaving the gun, to the utter loss of range and accuracy. Incidentally, gunners had to "run out" (push the gun into firing position) both smoothbore and rifled muzzle-loaders carefully. A sudden stop might make the shot start forward as much as 2 feet.
When the U. S. Ordnance Board recommended the conversion to rifles, it also recommended that all large caliber iron guns be manufactured on the method perfected by Capt. T. J. Rodman, which involved casting the gun around a water-cooled core. The inner walls of the gun thus solidified first, were compressed by the contraction of the outer metal as it cooled down more slowly, and had much greater strength to resist explosion of the charge. The Rodman smoothbore, founded in 8-, 10-, 15-, and 20-inch calibers, was the best cast-iron ordnance of its time (fig. 14f). The 20-inch gun, produced in 1864, fired a 1,080-pound shot. The 15-incher was retained in service through the rest of the century, and these monsters are still to be seen at Fort McHenry National Monument and Historic Shrine or on the ramparts of Fort Jefferson, in the national monument of that name, in the Dry Tortugas Islands. In later years, a number of 10-inch Rodmans were converted into 8-inch rifles by enlarging the bore and inserting a grooved steel tube.
THE WAR BETWEEN THE STATES
At the opening of this civil conflict most of the matériel for both armies was of the same type--smoothbore. The various guns included weapons in the great masonry fortifications built on the long United States coast line since the 1820's--weapons such as the Columbiad, a heavy, long-chambered American muzzle-loader of iron, developed from its bronze forerunner of 1810. The Columbiad (fig. 14d) was made in 8-, 10-, and 12-inch calibers and could throw shot and shell well over 5,000 yards. "New" Columbiads came out of the foundries at the start of the 1860's, minus the powder chamber and with smoother lines. Behind the parapets or in fort gunrooms were 32- and 42-pounder iron seacoast guns (fig. 10); 24-pounder bronze howitzers lay in the bastions to flank the long reaches of the