These Confederate soldiers are well armed, with imported P53 Enfields rifled muskets (3-band) and locally made Cook & Brother rifles (copied on the P56 2-band Enfield but with furniture wholly in brass rather than steel). Some of their accoutrements are also British, like the cartridge box carried by the soldier standing in the middle, in his shirt sleeves. Unlike with the American boxes (like the one used by his comrade lying at his feet), soldiers were not in fact supposed to grab ammunition from them in the heat of battle. They were only meant for storage, while there was a special "ball bag" to be carried on the front of the belt to be used for loading, which the Americans that received them discarded and used for the leather.
As I experienced as an ACW reenactor, using these boxes slows you down, a clear disadvantage when using muzzle-loaders, as they open only with difficulty.