You can get a proper 4500psi fill for $5.00 at Show-Me scuba (aka Aqua F/X) in Springfield MO. I had to get my carbon tank filled while i am on the road for work and this gentleman took care of me. You may want to give him a call ahead, it's a one-man shop so he has to step out sometimes. He also has a running contact list that local airgunners use to contact each other and sometimes arrange shoots. His website: http://www.sho-mescuba.com/