if you only get that pump in your forearms when using a tight grip, theres your solution, and therein lies the problem. loosen your grip a little bit man!
unless you are specifically training your forearms, you only need enough grip to allow to you to perform the movement effectively. as often as possible when doing movements like doing BB benches, press machines, BB curls, i dont even close my hands all the way around the bar (note: for safety's sake, when doing bench presses, make sure you are experienced enough to still be able to keep weight from falling when doing this).
what alot of people don't realize is the simple act of just pushing into the bar on alot of these movements causes enough force and friction to hold the bar on its own, without you having to use an excessive grip.
I also suggest trying curls "broken wrist" style. hold the BB or DB in your hands and allow your wrist to completely relax and "drag" behind the rest of your arm, it will keep your wrist flexors out of the movement and hit the biceps harder.
Yes,
NO-Xplode is supposed to help with pumps. People will tell you otherwise and say that arginine is still unproven, but i liked it when i used it. the most important thing if you are trying to concentrate on feeling pumps in the "right" place is working on building a strong mind-muscle connection