Is there some guide out there that might help me figure out which guns and ammo to carry and use? Its hard to know whether e.g. 20 gauge is better than 12 gauge or if its the other way round. Or which sorts of ammo I am most likely to find out there. Or for that matter, where to get ammo parts if I need to turn one kind of ammo into another at a reloading bench (or is tearing down ammo the only way to get the parts?)