Keeping gas mags warm in winter is always a problem. Hand warmers could be the answer!
If they are too cold your gun under performs. The 'o' rings can shrink causing gas to vent off. Having an empty gas mag at that vital moment could spell disaster.
Placing hand warmers in your magazine pouch will keep them up to temperature and ready to use. The day before a skirmish heat the hand warmers in the normal way. Allow them to cool overnight. Remember many airsoft gases are flammable. Use the cooled hand warmers to line your magazine pouch, keeping the mags at optimum operating temperature.