Cap boxes were for percussion (musket size) caps no matter what branch of the service you were in and worn on the belt on the right front. No ammo was carried in these till the metallic cartridge era when revolver rounds were carried in these. There were several variations of cartridge boxes for musket cartridges. Calvary generally wore a different type cartridge box specifically for carbine ammo on the belt. There was a box issued just for prepackaged pistol ammo which was worn on the belt. I suspect a civilian had his extra rounds in his saddlebags.
