.22's do seem to ricochet a lot. However they do have a lot going for them though, mainly that they are cheap as dirt to buy and shoot. The Marlin 60 is a fun little gun and very quite accurate as well. What you might do is get a light high speed hollow point that would breakup upon impact with anything.
Another caliber you might consider is the .17 Its rather new but I've heard a lot of good things about it as a varmint caliber.
.410 is a good choice.
A 12ga is a lot of gun for dispatching bunnies, hard on the ears and shoulder as well. A bit on the overkill side IMO.
There are a lot of airguns on the market that would more than dispatch a rabbit, but the trouble with them is they are usually single shot spring guns that need to be loaded and recocked every time which, if you have a lot of bunnies, might get tiring. But if you are just shooting one or two at a time this would work. There are quite a few on the market though that will push a .177 hollow point pellet at 1000fps+.
Here's my latest little toy I picked up over the weekend at the Wanenmacher's gun show. 30/30 so it would be a bit much for bunny hunting though.
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