Most of the time they are labeled that way out of liability. They didn't go through some FDA inspection or something that costs a lot more for the food grade stuff.... although the food cartridges and the pellet gun cartridges sometimes are the same size and came out of the same machine just painted differently after some inspection or another.
Another reason is regulation. Since some of those cartridges can have several hundred pounds of pressure in them, playing with a 'non food' grade cartridge, in other words putting a cartridge that might not be the exact fit into something and having it come flying out as a missile hazard, this keeps them from the lawsuit due to your stupidity. Or you making something of your own, and pumping that 900 psi cartridge into your one liter soda bottle because you did not have the common sense to regulate it down to say 20 psi or whatever and the bottle goes boom and rips up your hand.... saves them from the lawsuit.
Im not sure on the silicone based lubricants imbedded in the cartridges. For an air rifle, while they do need lube once in a while, this might cause problems with gumming up. Ill have to go look at that one, im curious now.
Aaron
