Whenever you find a can of duster, check the warning label on the back (first aid treatment and such). This is generally where they will tell you if it's diflouroethane or tetraflouroethane. Di is lower powered than tetra, is the main reason you are encouraged to find the tetra instead. Never heard of di attacking your O-rings, but I won't argue with that new peice of info.
Still, when you buy a new can of such and such a brand name, check the label again to make sure it's still tetra, sometimes a company will change the compound due to whatever reasons. Saw it once, so it happens.
Also, electronics stores sell freeze spray (for cooling off electronic components as a means to troubleshoot). Anyways, duster is held upright and when the trigger is pulled, the gas vapour is spewed out of the nozzle. Freeze spray has the liquid shoot out since there is a straw inside the nozzle. You can use freeze spray, but have to fill your mags right side up, otherwise if you try it upside down, you'll just get a fill of gas instead of liquid (which is what you want, the mag just becomes another container for the liquid).