While a punch can form a simple heal on a bullet, it can not form a waist, or indent around the bullet. That is to say, if a grove for the case rim to crimp in to is desired, a common LSWC swage punch won't do. The question isn't clear about just how much of the 'sphere' is desired. Up to 50%, no problem... 51%, where the sphere starts to get smaller, big problems.