I dug around a bit and found my 30/30 dies and gave this a try. It works. 40 S&W into 8mm Nambu. Cases are a bit long and should be trimmed. Compared to my one original Nambu cartridge, these are longer and have a thicker rim. Rim is a little bigger and so is the base of the cartridge case, just ahead of the extractor groove. It took a lot of pounding getting each case out of the die after forming the base. CH Jr Champ has compound leverage so it wasn't that hard forming them. Tried Imperial lube, then went to lanolin. In my RCBS primer pocket swage set there is a cap that fit over the ram nicely. Tomorrow, I am going to trim them and see how they fit in a gun.