It all depends what kind of look you're going for and what you're painting over. Is this a wood or synthetic stock?
Rockerguard or bedliner paint seems to be popular. I've used it on vehicles but never on a gun stock. There are some good brands and some cheap brands. Most of these types of paint would be reasonably durable if you're looking for the textured matte black. A good bedliner would be more durable than rockerguard. Surface prep would be pretty simple and forgiving. Give it a rough scuff with about 120-400 grit. As with everything, it must be superclean and degreased.
Plenty of guys have used krylon fusion on synthetic stocks and have reported good results. I've never used it because I don't like rattle cans. There are a lot of good pictures on this forum of camo jobs using this paint.
I paint stocks using automotive urethane enamels. These are 3 part catalyzed paints that require proper spray equipment. Before painting I usually sand/scuff with 400 grit. For a synthetic stock I lay down epoxy primer, then whatever base, candy, or clear. For a wood stock I've been painting candy then clear. Usually about 10 coats total. If you want more details let me know.
dh