Some tips regarding filling off a large tank:
Turn the tank upside down so you get liquid CO2 and open the valve slowly
Freeze the empty bottles so they don't vaporize the CO2 as they fill and you can get a full fill
Weigh the empty bottle and fill to tare + amount on the label or when it warms up it'll blow the pressure release. Its pants-shittingly startling when they blow the seal and it's on the passenger seat of the vehicle you're driving and fills the cabin with CO2 fog.