RE: 12G / 00 Buckshot / Drop
There won't be any drop at 30 yards. I've used to shoot buckshot all the time when I lived in a state that allowed it for deer. My shotgun shot it best with a full choke, but you may want to take some other choke tubes with you to the range just in cast your gun likes them better than the full. Also take a few different brands of ammo with you to see which one patterns the best. If your gun patterns tight enough, you may be able to safely shoot astep or twofurther than 30 yards, but when you don't know what kind of actual performance you're going to get, it's best to limit your range. You want all the pattern density that you can get, put up a kill zone sized target and shoot it to see what kind of damage you're going to see on an actual animal, that'll give you an idea of the actual limitations you're looking at.
Buckshot is deadly, but not if you try to force it beyond it's limits.