Confederate forces destroyed Harper's Ferry Armory in Virginia at the beginning of the Civil War (1861-1865.) The Springfield Armory in Springfield, Massachusetts, thus became the only United States government small arms factory. Springfield rifle-muskets like this U.S. Model 1861 became the most popular weapon of the Union infantryman. The spiraling grooves, or 'rifling' on the inside of the barrel forced a new style bullet, called a Mine ball, to spin as it was shot. This meant that the bullet went farther than the old smoothbore muskets of the American Revolution and War of 1812. A cap that lighted when hit by the gun hammer replaced the old flintlock system. The Union could make ammunition and weapons in far greater numbers than the Confederates could produce because they had more workers and a better factory system.