I actually do a whole exercise regimin everyday to keep building up muscle mass in my forearms and to improve my grip.
My biggest problem right now is holding the pistol out and keeping it on target, after a while the target just doesn't stay perched on top of my sights - it's swerves all around like a crazy UFO.
But building strength in my arms makes that situation better.
Here are the other exercises I do:
Hammer curl:
http://www.exrx.net/WeightExercises/...ammerCurl.html
Ulnar dumbell:
http://www.exrx.net/WeightExercises/...arFlexion.html
Wrist curl:
http://www.exrx.net/WeightExercises/...WristCurl.html
I also do the crush grip:
And wrist roller:
