Use a G.I. ammo can. Dunk it (empty) in hot water to check for leaks. Leave it there long enough to warm up the air and build a bit of pressure.
Pack it on the coldest, dryest day of the year. Toss in a dessicant pack and seal it up.
Store in a cool, dry place. 60 Deg-F is great. Never above 85 Deg-F. Beware of basements--if it's damp, you can have the ammo can rust through on the bottom (where the paint wears off) and never know it until too late. Inspect every five years and renew the dessicant. Always do it on a cold, dry day (or night).
After ten cycles of this routine, fire 100 rounds and you shouldn't have even one misfire.
