Artillery Through the Ages (Illustrated Edition). Albert Manucy
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.
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