It seems to me that liquified CO2, which is what will be in those disposable bottles, is about 900 psi at room temperature. Of course, the pressure will vary with the temperature of the CO2.
Pressure in CO2 bottles should be the same for all bottles at the same % fill. As for the volume jut fill it with H2O from a large syringe and see how much it holds. If you cant find a syringe with volume markings mark where the plunger is before you fill the cartridge and then refill out of a graduated cylinder.
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