A Glock 20 is definitely the lightest one you could take out there for sure. And as others have said, you get 15 rounds of 10mm, which is a lot. You could go with a 45 or 40 and I'm sure it could kill a pig too, but not nearly as easily as 10mm. A 40 S&W round is just a 10mm cut to about 2/3 length. The 10mm has a lot more arse behind it.
As much as I dislike Glocks, I think it would be your perfect candidate here. It doesn't matter if you got it dirty from working, it has a polymer frame so it weighs less, and you get 15+1 chances to drop that sorry arse pig. Image: http://www.tactical-life.com/online/wp-content/uploads/2009/03/glock-20sf.jpg
But if you instead decide for revolvers, as others have said, a Ruger GP100 or S&W 686P (7 shot) would do the trick.