I have been using CO2 to speed up load development for over a decade now. I was fortunate to have a cooperative welding supply shop let me try several regulators till I got the flow I needed. Some regulators do have enough flow to work.
A friend tried a 5 lb CO2 tank and found out it was too small. IMO 20 lb tank is minimum.
A rubber hose is attached to the regulator. The tip of the hose is cut into a taper. I always wipe off the hose before inserting into the chamber. The valve on the tank is fully opened then the regulator is adjusted for enough flow to cool but not waste the gas. It only takes 15 seconds on thin barrels. I feel the chamber and some of the barrel and turn off the gas when it gets close to ambient. It will continue to cool after gas is turned off.
One guy came over to see what the hissing was. He asked is that oxygen? I said yes I was trying to accelerate the wear on the throat.......