From the 1840s through 1870s, after which time metallic cartridges vastly replaced the Percussion-Cap system, small ribbed percussion caps were made for pistols. I dug a capbox full of them at the Spotsylvania Courthouse battlefield. That exact same form and size was also used in civil war artillery Hotchkiss and Schenkl Percussion fuzes. So, I wouldn't discard this one as being modern-made. I don't think they can be told apart, unless there's a maker's-marking on them.