I ran a classic on CO2 for years, even without an expansion chamber. It worked great. I did have an anti-siphon tank, but it was tilted at an angle to minimize liquid getting into the tube. If you are using a horizontal tank setup, so not use an anti-siphon tube in your tank. Running your air line through a fore-grip is better than running directly to the valve but not as good as through an expansion chamber. The larger volume in the foregrip does help keep the liquid out.
Except for the Automag in front, its usually the man behind the equipment that counts.