I'm hoping someone can basically tell me I'm being an idiot, I'm right, and I can move along. Alternatively, I think maybe someone might tell me that the tank doesn't actually hold 20 oz and I should assume it's going to cut out well in advance of my logical answer below:

I have a 20 oz CO2 tank. 1 ounce is 28 grams, so 20 oz should be 560g. The whole tank full weighs 1374g. Can I assume I can run it until 1374 - 560 or 814g or is this a poor assumption. Will the gas cut out before then? How much before then in your personal experience?

More importantly, rather than tell me my math and logic are right... can anyone confirm or deny this BASED ON EXPERIENCE WEIGHING THE TANKS BEFORE AND AFTER USE?

Thanks in advance to those giving input based on personal experience.