I totally agree with you guys, weighing the tanks would be a great idea. But when the topic comes up with management, it's always shut down because our filling system is so smart it knows when to shut off. Well, that's not true, it just knows when to shut off when the tank is filled to a high enough pressure, which is supposed to be at around 85% for safety reasons. A 20 oz bottle is supposebly designed to hold a little more than 20 oz to allow for expansion and stuff. So the system is designed to fill 20 oz into the tank and there is still some room left after.
This is what the Brass Eagle reps. tell us, because we use their system. I'm not sure how reliable the info is, but it's all I have to go by.