I was planning on making a compressed air gun using a culligan water jug. I'd put a bicycle valve stem in the bottom of the jug and us a valve on the top with a barrell attached that has the diameter to shoot golf balls. I know this has been done before but I've never seen a water jug this big used. My question is this, is there a formula you can use to solve for feet/second by plugging in weight of the ball (45.93 grams) and psi level used to shoot the ball? I don't know the psi the jug is capable of holding yet but could someone solve it by plugging in 100psi and then again by using 200psi. This may be a very easy problem for most of you. I think I would have been able to figure it out a couple months ago in school when learning this type of stuff, but I forgot it allready. Thank you.