I use the heavy ones. They work good for everything I have used them for.
Consider buying, or making a "Pogo". I rarely use my slide hammer and made myself a pogo, and use it all the time. It allows you to apply gentle upward pressure along the crease, while massaging the high spots around the crease downward.
Make sure that the stud holder and copper ring are clean as that is the circuit. And..........Practice on a similar gauge metal prior to your project to get the feel as to how long to pull the trigger. It doesn't take much. Good luck.
Oh yea.........If you are going to apply several in a row, make sure you cool the metal with compressed air as you go. The metal will do all sorts of weird and wonderful things if you don't.
