Where do you guys get your co2 tanks filled? I use a guy in Brooklyn but i always think that i am being "short-changed" ........my first 10lb co2 tank read 800lbs pressure and lasted roughly 4 months, my recent exchange, the tank is reading a hair over 500lbs pressure and the tank itself feels "light", the guy said that it is an aluminum tank which weighs much lighter than the traditional tank. i just want to have someone else to use for comparison.