Everyone has their own opinion on the best varmint gun, but I think you'll be happy with the .223. You also can't go wrong with a model 700 Remington. A friend of mine had a custom .223 gun built on a model 700 action, Choate Ultimate Varmint stock and a Douglas 1 in 8 twist barrel. He routinely kills Groundhogs at 500+ yards.

I have a custom AR-15 Flat-top with a Douglas 1 in 8 barrel, a Leupold M-3 Scope and a Milazzo trigger. It is also accurate well beyond 500 yards on small game.

The benefit of the .223 is that it is the current caliber of choice at NRA High Power matches. This means that every company is striving to provide upgrades for these weapons. It is the only .22 cal out there that has an almost unlimited number of bullet grains available... all the way up to 80 grains. With the right gun and at least a 1-8 barrel, you can shoot accurately to 1000 yds with 80 grain hand loads. Good luck on your choice.

Semper Fi, George