This is often referred to as a typical "toilet seat" cap box. Popular around 1850-1870 give or take a few years. It was used more for percussion caps than for patches so I have always called it a cap box. I have seen them on rifles from New England to the midwest and into the far west. Tim, something to remember, to find a late flintlock rifle with one of these boxes is a pretty rare bird. Nearly all were percussion.
