Speaking as a field manager with 29 years of experience in this industry. We use a table top scale...specifically an ultra ship 35 from a web site called old will knott scales. here is a link http://www.oldwillknottscales.com/se...hip+35&x=0&y=0
The scale is primarily used, outside of paintball, as a postal scale i.e. weighing letters and packages. It has multiple settings Grams, Kilograms, Pounds, Ounce, we typically use the ounce setting and what is called the mailer tube attachment. this prevents the co2 bottle from moving around.
The hanging scales are not accurate due to the liquid moving through the line and inside the recieving vessel or the bottle. If you ever watch a bass tournament the weigh in at the end of the tournament uses a table scale while on the boat they will use the hand held to get an approximate weight per fish. The squirming fish makes an accurate read nearly impossible as does the liquid "sloshing" around the bottle.