I like iether a 12 g shottie, a .22 Hornet or 22/250 for feral cats.

I have shot one with my cz .416 Rigby loaded with woodleigh 410 gr softs at a range of 10 yards directly up the poo chute and it literally exploded

Ah yes, the old Cat-ass-trophy by Rigby. It's odd though no less spectacular; when your sear broke the cat became very much more valuable than before. I'm not sure I could afford a regular diet of Rigby pureed cat, but it is good that some can.