I think of it as brain freeze. I like Torg's idea of different ammo mods but then you would need to carry 3 different guns I guess. As long as they didnt weigh too much (compared to the spell variants) then this might well work. However knowing you are going to strip off the blue shield every time might just leave the other 2 up would just be the same as the ppu spells. I cannot decide if I like this idea (simplicity always appeals) or prefer the random shield.

Either way its a great idea!