On gauge, it seems likely that's what the "-10" means in the markings on the tool.
Still having a bit of trouble visualizing what this thing does. From the pictures Mark posted (thanks!) it functions like a crimping die for conventional metallic cartridges, by reducing the diameter at the open end with a "shoulder." But note that the shell in the cross-section diagram has no cushion wad, which leaves the load column short and a good length of empty hull at the mouth for the crimp. And the tool in the illustration has no slots like the one on Ebay.
It seems like the slots are there to provide a "ripple" to relieve the strain on the crimp--meaning, it doesn't "roll crimp," it "pleats" the end of the hull like a modern metallic blank or grenade-launching cartridge.
Is there a good reference book that covers all this stuff? I'm very familiar with modern cartridge reloading (have loaded both BP and smokeless for many years in many different configurations), but there are some pretty strange-looking gizmos associated with loading old shotshells. Pulled out my copy of Greener's "The Gun and its Development" and found a picture of what I thought this thing was doing (see shell casing in the picture, below). The tool in this illustration is beefier, for crunching brass rather than paper.
