In order to get big pumped shoulders my favorite exercise is the behind the neck shoulder press. I do it in the cage.
The trick here is to take the weight off the pins, have the bench as high as it will go to support the back. Start at a low weight and pyramid up.
Only go parallel with the bar behind your neck. Your just chancing injuring your shoulders if you go lower. Be sure and have the cross protection bars a little lower then your shoulders. I do about 4 sets with the last set at about 225lbs for a set of 8 to 10.