OK, so I have this Little Scorpio survival shotgun and I wanted to make a gizmo that I could throw in the GH bag with the shells that would allow me to make cut shells fairly easily. So I came up with this. Simple gadget to make two symmetrical cuts to most of the shell casing creating my cut shell.

A couple of things to consider: ~ I'm using this in a break-action so I won't have cycling issues. The same cannot be said for any action that actually cycles (pump, semi). These won't cycle properly so don't plan to use them as such.
~ Obviously the shell is destroyed upon firing (no reloading afterwards). ~ Cut shells are an emergency substitute for a slug. Imperfect at best.
~ The cut is happening at approx 22 mm from the base. You may need to adjust the design based on whatever shells you are using. Test before relying on them.
~ Keep in mind the shell will want to spin while cutting - you need to hold it firmly to prevent this if you want the two symmetrical cuts.
~ Finally, never cut your shells ahead of time and store - you are allowing moisture/air into the section of the shell that holds the powder. In adverse conditions, you could end up with a dud and that's not cool.