One of the biggest is his stand on firearms. He runs around doing photo ops with shotguns- including some really bad gunhandling- and telling everyone how he loves to hunt (how many people hunt deer crawling around in the woods on their belly?). But, if I'm not mistaken, he's voted for every gun ban, tax, restriction, license idea, etc., that has come through the Senate.
On the subject of the Assault Weapons Ban, may it rest in compost heap, he made the standard comment about "you don't need a machine gun to hunt deer", along with various other crap. The Second Amendment doesn't say a thing about hunting, it speaks of the right of the citazen to arms. And the AWB had nothing to do with machine guns; the National Firearms Act of 1934 does that on the federal level.
And he's been right in the middle of that load of crap that "we don't want to ban guns, we just want common-sense safety laws" that always involve banning or licensing or otherwise restricting ownership of arms.
If you aren't familiar with how various states/countries gun control laws have worked out, as far as crime goes, check out Smallest Minority. The man has done a marvelous job of tracking a lot of this stuff.