OK, I grabbed a C02 cartridge and slapped it onto my keg - before reading the "not for human consumption" warning . Is my beer ruined? I popped it off, and sampled a glass - didn't notice any off flavors. Will hit the homebrew store on Friday to pick up the "human-safe" ones...
That's because CO2 isn't safe for human consumption! It doesn't have any meaning in relation to the contents of the cartridge other than that.
That's a good point. However, the Crossman cartridges are stamped stating that they contain oil. I assumed that's what he was referring to. Way back in the day (mid-90s) I used one or two of those to dispense a mini-keg (or several) to no ill effect. The quantity of oil that might actually wind up in the beer has got to be minimal, especially in a 5 gallon keg. Nonetheless, there are better options and I don't recommend using the wrong type of cartridges.
You ought to be able to get good cartridges at any kitchenware place that sells whipped cream dispenser or soda water chargers. You could also use the nitrogen cartridges to dispense, but they tend to be shorter IIRC.