Yes the slapper is used because of the larger surface area.
[IMG]http://inlinethumb12.webshots.com/38795/2245504680102553149S600x600Q85.jpg[/IMG][IMG]http://inlinethumb33.webshots.com/36640/2614690920102553149S600x600Q85.jpg[/IMG]A hammer because of the smaller surface area many times can cause damage simply because of size difference between hammer and dent.
Secondly, a hammer has a smaller "sweet spot" thus making it harder to hit the dolly directly.
A slapper because of the larger mass can move metal quicker and faster when needed. It can also finesse the metal because the larger area acts like a cushion sorta speak when doing real light taps.
For moving the metal quick and fast I have a slapper that weighs around 7lbs its a friggen monster. Not something you want to use all the time, it simply weighs to much, but there are times when its a must.
[IMG]http://inlinethumb23.webshots.com/47126/2198529700102553149S600x600Q85.jpg[/IMG]Its from an old truck leaf spring and about 1/4 thick
[IMG]http://inlinethumb17.webshots.com/28176/2322177000102553149S600x600Q85.jpg[/IMG]This one is made by Ron Covell but he no longer makes or sells them so you cant get them anymore. This one weighs alittle over 2lbs and my main slapper.
[IMG]http://inlinethumb28.webshots.com/46299/2302620890102553149S600x600Q85.jpg[/IMG]With a tape measure
[IMG]http://inlinethumb37.webshots.com/45796/2473992230102553149S600x600Q85.jpg[/IMG]
