If your goin for pure carnage a .220 swift is pure magic on pdogs if your looking cheap a good scoped .17 hmr can be quite satisfying a .223 is the in between I used to load high velocity varmint grenades they are fun I also reloaded some 55gr .243 rounds that were awesome and comparable to the swift, of course the 22-250 is also very fun the .204 is also a good round with no recoil. In my experience velocity is the key for carnage I used to guide hunts and anything kills and is fun but the after shot comments from the swift were priceless lol