I can't tell from the photo - maybe .38 Special, .357 Magnum, .38 Short Colt, .38 Long Colt, 9mm Parabellum, 9mm Federal, .38 ACP, .38 Super, .38 S&W, and maybe .380 ACP, if you put a rubber O-ring in the extractor groove to act as a temporary rim (which I've read can also work with shortened .223 cases, and maybe some of the rarely seen European 9mm cartridges, like 9mm Bayard, 9mm Glisenti and 9mm Steyr ;>). Plus maybe 9mm Browning Long, and possibly others like 9mm Makarov and .380 Revolver, if you reload your own cartridges with bullets of smaller diameter. And I'm probably missing a few - it might depend on your personal tolerance for bulged or split cases, etc...