Perhaps I misread some of the comments in terms of their intended tone. Understand that my consternation comes from my upbringing, for I was raised to believe that life is precious and rare in all its forms and that the killing of any animal carries with it a significance.
And I'll admit that some of my reaction comes from liking cats. I like their independent natures and admire their hunting skills. I have an indoor cat and recently started feeding an abandoned outdoor cat, who has now taken up residence at my house. This was no feral cat, mind you. This cat is people-friendly and clearly abandoned. Here Art, I share with you an intolerance for folks who don't take care of their animals. This cat has since been fixed, tested for disease, and given his shots.
Feral cats are another problem entirely. The animal control department in my town recently had a big cat "roundup" in one particular neighborhood where the feral population had gotten out of control. Seems that when it rained and then the sun came out, the whole neighborhood smelled like cat urine. Yes, many of the rounded-up cats were euthanized. And shooting the cats, if carried out humanely, is really no different I suppose.
I would hope that folks here would be sure of two things before they pull the trigger though.
First, make sure it is a feral cat and not someone's pet or an abandoned animal. If the cat will approach you, it may have been deserted by its original owners. I think the better option here would be a humane association or pound. At least the animal would have a chance at a life.
Second, make sure the shot is instantly lethal. If you're going to kill an animal, I think there should be some honor about the act. A quick and painless death is something any of us, human or beast, deserves. Use enough gun and be sure of your target.
I have heard my fair share of cat-shooting comments at gun shows--particular with regard to the Colibri .22 rounds (some call them "cat rounds"). In some of these voices, I've detected a jubilation at the prospect of inflicting injury on random cats. There is a glint of meanness and an uncaring tone that disturbs me there, and perhaps I was projecting these voices onto the above posts.
I know I took this thread way off topic, but I felt like the ethics of shooting a cat needed some attention. In response to the original question, I think that .22 FMJ could be a cruel round. Look for a round that offers quicker expansion and therefore a greater chance of a humane kill. There are lots of good hollow point rounds in .22 caliber, but still, shot placement is critical.