Got 100 of the Starline cases on order. This question was just due to having five boxes of once fired Federal factory .30-30 ammo on hand and no .30-30 to load them for. (I know, get a 30-30!) Right now they're just sitting on a shelf so I was exploring how to possibly repurpose them.
I have an 8x57 FL die but that's the biggest expander on hand, except when the .38-55 dies come in when I'l have a.375 expander. Expanding necks form .30 to .32 is easy enough but not sure if the cases would make the jump from .32 to .375 in one step even with the inside slicked up with Imperial Sizing wax. I might try one just to see, though, since it would be easier than running out to the boonies to try a fireforming load that may or may not work, then coming back, adding more powder, etc. But I do have all of the ingredients on hand - Unique, thousands of large pistol primers and even Cream of Wheat.
Looney questions, mostly. "I wonder how this would work...?"
