Just a thought I had the other day, but does anyone know of a rechargeable CO2 canister out there on the market? All the ones I've seen are single-use, throw away jobs.

I'm thinking it wouldn't be that hard to make something about the size of a 40g cartridge that can be re-charged (to say 100-150 PSI) by using a floor pump just using regular air. That way you don't have to keep buying cylinders (and adding them to landfill), and you'd always have a free source of compressed air for either home or track use.