Friend has a farm in Northern Kentucky,we weren't finding any rabbits like we used to.His dad ,whose the county vet, pointed out a huge brush pile in between two hills on the property that was overrun by feral cats.One afternoon we took a cooler,sandbags,and some AR's and made a afternoon out of it.Now an ex and his wife asked how we could shoot a poor cat?I said easy just put the cross hairs on it and squeeze.I also told them to go check out the ones with the mange and inbreed birth defects.
To answer your question in an open area .223 is nice,.300 Win Mag with 125gr. hollow-point is also spectacular but grossly overkill,as we found out.