vinegar and baking soda will do the job but if u already have the co2 bottles ya may aswell rip a few open every now n then, they're only like 80pence each anyway and im sure u will get more enjoyment from blazzing up than shootin beer cans, even more enjoyment when blazzing up and shooting beer cansyes u can but it will get pricey.also viniger and baking soda in a bottle will work