The 16 gauge shotgun short chamber is fairly simple to deal with. I have a combi gun with a 65mm chamber, I buy 2 & 3/4 inch shells and use a purpose made cutting tool I found on the Internet to cut off the crimp at the very top of the shell body. I then have a very thin cardboard disc also found on the Internet for 16 gauge shells that I place on top of the pellets and then roll crimp the shell mouth in a drill press. One will need to lighten the shot charge ever so slightly to make room enough to roll crimp, but it works like a charm! Instant 2 & 1/2 inch shells!!!

The odd rifle caliber situation is remedied by finding brass and or modifying existing brass through some creative resizing. This is a much more challenging item to overcome based on the caliber chosen. And I'm assuming some advanced reloading skills for the rifle cartridge.