People have differing opinions. Personally I wouldn't advise storing them completely full since temperature changes could stress the seals. On the other hand you should definitely keep alittle gas in them to keep the seals lubricated. I usually keep enough gas in mine for 2 or 3 shots and that keeps them in fine shape. Really the only time you want a gas mag completely empty is when shipping them, since the pressure changes at altitude can cause damage otherwise.