The .223 Rem will do the job from just about any rifle on that size target at that range. The ammo is cheap and readily available and you can play with it if you're a handloader. A lot of these varmint rounds are pretty exotic and hard to find...not to mention expensive.
I use the .223 for medium sized game (coyotes, coons and possums) at ranges out to 300 yds or more from a Ruger Mini-14 topped with a NcStar 3-9X scope. I really like the Wolf varmint rounds with the red plastic tip. They feed reliably and expand nicely without causing too much pelt damage. They are affordable and the quality control seems pretty consistent. That's always important with an autoloader. Good luck!
I agree with the above post. The 223 rem will be excellent for what you need to do and the ammo is everywhere. 22-250 may be another caliber that fits your situation for you to look at that is easy to find ammo for. It is more powerful and flatter shooting than the 223. Out of all these calibers, we are not talking about a whole hell of a lot of difference one way or the other.
In the darkness, the hunter stumbles through the underbrush, making noise and leaving his scent seemingly EVERYWHERE!
Daylight will be here in 30 minutes and he wanted to be in the stand an hour before daylight.
"I know I left that stand RIGHT in this area last night," he mutters under his breath, "but where is it now?"
He traipses back and forth in a zig zag pattern, getting himself overheated and sweaty, but never finding the stand he left there the previous evening – and eventually sits on a...