One of the most important of the Confederate industries which the novel’s fictional Quartermaster Major Clayton Ellis supervised at Knoxville was a copper rolling mill. It made percussion caps to fire the army’s rifled muskets:

“The cap contains fulminate of mercury, a chemical compound which explodes when it is struck. This is the same stuff as is used in the paper or plastic caps in a child’s cap gun….

“When the cap is struck by the hammer, the flames from the exploding fulminate of mercury go down the tube, into the gun barrel, and ignite the powder inside the barrel to propel the bullet.”

All of which is graphically demonstrated by the animation at the link. Wait a few seconds for it to start.