Jim,
My cousin uses shortened 7x57R cases I gave him and they work well.I had some in my "junk pile" made from 303 British cases that also worked ok,while a little smaller dia. I use 444 Marlin cases for carpenter bees in a 2 1/2" 410 pistol. I suggest you cut overpowder(use 2or3)and overshot wads from the bottom of the trays meat comes packed in.I seal mine off with Titebond II, and my cousin uses waterglass. It all works, but the longer cases have more capacity.
Mike