Ok, I recently got an iSi Soda Syphon. With it I ended up having to buy iSi CO2 chargers, which ran 10.99 plus tax for a carton of 10- 8g chargers. Cheapest I found them was 9.99 online for an off brand. (Some places list 6.50 but then make up for it with shipping.) So about $1-1.20 apiece when all is said and done. Walking into the sports section of my local big-box, though, I see 40 packs of 12g chargers for pellet guns selling for $23. Makes it about $0.60 each after tax with 50% more CO2. Question is, any reason I can't substitute? Before you mention the amount of CO2, iSi allows for double charging the canister if you reduce volume from 32 to 26 oz of water, so we're OK there. I am also aware that there is, at least technically, a difference between food grade and non-food grade. In reality, though, is there any harmful (as in health... I'm willing to test for taste myself) gas that could make it into non-food grade CO2 or is the distinction, in this case, illusory? Jim