RE: 20 guage buckshot Vs. 100 pound hog
yes they do make many different types of slugs for 20 gauges, in fact some people are shifting away from using 12 gauge slugs and using 20s because they don't beat you up with recoil as bad and still hit deer like a truck. I would imagine they would do just fine on a 150 lb hog as well. Depending on whether you have a rifled barrel or a smooth will change the ammo you use and the effective range. For a young guy I would stick to just the basic foster style slugs and keep your shots fairly short and it will do just fine.