In 1939, the 30 Carbine was developed for use in a light, compact battle-rifle, designed by Ed Browning (half-brother of John M. Browning) and David Marshall (Carbine) Williams — while the latter served time in prison. The 30 Carbine is a medium-pressure tapered cartridge of about the same length as the 357 Magnum. Performance was limited because pressure was kept lower than it might have been and because capacity is limited. Chambered in a revolver it can launch 110-grain bullets at about 1500 fps, compared to the 2000 fps it will generate in a carbine. Had the Military adopted a higher pressure-standard for the 30 Carbine, it probably would have garnered more support in the sporting-arms field. As it is, performance in a carbine is in a no-man’s-land of, too much for small-game hunting and not enough for big-game hunting while the gun it was chambered in generally do not have sufficient accuracy to be useful for varmint hunting. As such, the 30 Carbine has garnered limited acceptance and is, perhaps most useful as a handy case for wildcatting to smaller-calibers for varmint rounds, such as James Calhoon’s impressive 19 Badger. Considerable (mis)information(?) has been published regarding the derivation of this case. The truth is, it is unique and had no obvious precise predecessor. While resembling the 32 Winchester Self-Loading (WSL), it has a larger rim, is significantly larger at the base, and is tapered. I suspect the case used for gun development might possibly have been the 32 WSL. If so, that was only a temporary situation. The case standardized for the 30 Carbine shares no dimensions with the 32 WSL case. As with any round headspacing on the case mouth, best practice is to apply a taper-crimp after seating the bullet. This helps to lock the bullet in place against chambering forces that might otherwise drive it into the case. I cannot too-strongly recommend getting a second seating-and-crimping die so you can have one adjusted to seat the bullet and the second adjusted to only taper-crimp the case mouth. Generally, attempting to do both operations in one step is a recipe for damaged and destroyed cases.