they can be troublesome, i use a ball joint puller which i grinded a little to fit better, be careful though when hammering...ALWAYS put a nut on the thread first but DONT use the castle nut, they are not as strong due to their shape, use another dummy nut or turn the castle nut upside down.
Also make sure the nut is on far enough, if not, the threaded bolt end will bend due to the holes thru it which make it weaker..
Bottom line: Hit with caution. check for damage every 3 blows or so. make sure the thread doesnt collapse or else you cant get the nut off again and the whole ball joint turns!