I'm about to load some 40 cal shotshells. I will start with 10mm cases and use a die to put the shoulder on the case. Has anyone else done this? I am mostly concerned about the amount of powder needed. I typically use either Unique or 231 in pistol shotshells.
The actual loading will not be a problem since I have made shotshells for 45acp, 45LC, 357, 410 (from 303 Brit).
Hoping to get a little guidance and not reinvent the wheel.