I would think the most powerful would be a .50 BMG pistol

.50BMG is a massive rifle round and is waaaaay more powerful than any handgun round.
airbornecombatengineer.typepad.com...
airbornecombatengineer.typepad.com...
Supposedly a .50BMG revolver!
Now this is pretty dumb to say the least. Not very practical or even portable. Why not just get a real cannon?
[edit on 29-1-2009 by warpboost]