Revolver, the longer you collect the more unheadstamped mysteries you will see. Early U.S. BP sporting rifles Sharps Remington & such is just check full of them, also early US pistol revolver & case types that were common to early CF repeaters [such as 44WCF]. Plus lots of European pistol & revolver not to mention Japanese cartridges for various hand weapons.
So just because a cartridge is not headstamped don’t pass it up, the variations are seemingly endless & keep in mind some of these mysteries solutions don’t come easy or seemingly ever, but the search is great fun, you’ll learn a ton & make some great friends in the process.
My 2¢ for whatever that’s worth & just my opinion.
PS buy books some great information already in print.
Ken Elks has covered Japanese in great detail, if of more interest to you.
See the IAA site’s books listing.