I've run many different 'Cockers on CO2, but only in warmer weather. At cooler temps (under 50-60 degrees), you'll have a hard time sucking enough pressure out of CO2 to keep it running. My rule of thumb is if it's warm enough to play in short sleeves, I'll use CO2; any cooler and I'll grab for the HPA tank.
Also, regardless of how old or new, a regulator will help any Autococker to be more consistent. An anti-siphon tube in the tank or using a remote line will help as well. Expansion chambers aren't really going to help much (if at all).