The calibre thing is something that's pretty set in his mind. He had his old Original in .177 and was later talked into getting an Airsporter in .22. In his words it was s*not very good*! Mental block on that - he hates .22's!
Edit - No CO2 unfortunately. I was thinking about a Ratcatcher but he wants a break barrel. At 70+ he's set in his ways and that won't change!