Thanks to all who posted info on this board, have two great shooting rifles. Used a 13 CI HPA tank and 1250 psi regulator. The low pressure output has a 1.8K burst plug -VERY important for your safety. Get about 100 shots per pump-up, 2500 psi to 1000 psi. I am really happy with the quality of the QB's. Did change out the o-rings- they where damaged from the factory.