There are a couple of sights out there with step-by-step instructions and pictures. Google around a while and your bound to come across one of them. I wouldn't use anything bigger than #9 'cause we're talking about a 15yard MAX range. Besides, rats and snakes are about the only thing these are good for unless you have a custom smooth barrel. #9 will take care of those two critters just fine. Heck, I wanna say that one of the sights I'm thinking of used #12!!! (Not even sure if it exists...I know I've never seen it)