Very simple... Keeping the powder and caps in the original container,
Store in a Cool (room temperature) and Dry environment for both.
They can be stored in an Ammo can with Dessicant bags. Stable temperatures and low humidity are the key to shelf life.
Usually components are sealed at the factory with tape and/or lacquer.
Keeping the seals intact furthers the shelf life.
I have VERY OLD powder and VERY VERY old caps that have been stored in a favorable environment.... They both work like they were manufactured yesterday.
Never re-package either component, except to decant powder to a flask and caps to a capper for immediate use. Never mix components and date/label everything carefully for accurate future identification. (you may not be the person responsible for identification/use of the contents).
I cant perfectly attest to the actual longevity of powder and caps, but again I have used properly stored components from the 1930's and they worked like a charm.
