Old school Shockers run great on CO2. They were designed in the days before this new fangled compressed air had caught on in the mainstream market (Jesus, I sound old for 19), and they were designed to work with it. In fact, in their heyday, a lot of people would get giant 88ci bottles and fill them with CO2 to use on the Shocker because they could get so many more shots. Because they're LP and not real efficient, the shoe boxes suck compressed air like a vacuum. Since CO2 is stored as a liquid, you could get a lot more shots from the same volume of CO2 as compared to air.