The OP asked me to chime in so this is my advice.
The best environment to store your motors in is a cool, dry place, as both heat and water can alter or react with the chemicals in the propellant.
The major culprit is water (humidity) as it will react with metal fuels and eventually oxidize them. Aluminum and magnesium are the most common metal fuels used in rocketry. Both make the combustion hotter and the magnesium make the propellant easier to ignite. Aluminum burns to form Al2O3 and magnesium burns to form MgO. In storage H2O can slowly react with Al to make Al(OH)3 and some H2 and when heated Al2O3 with the elimination of H2O. Similarly Mg slowly reacts with H2O to make Mg(OH)2 plus H2 and when heated MgO with the elimination of H20. This is the white stuff you sometimes see on high aluminum propellants. Since oxidation already has occurred, an oxidized propellant grain will be hard to ignite and initially burn much slower than an identical propellant grain that has been stored in a dry environment. The same thing happens with the metals used to make colored flames, and the ionic salts that are also used for colored flames are hygroscopic and will form hydrated crystal which have a larger volume than the original crystal and can debond from the binder so keeping your motors in a dry environment is the best why to insure that they will work properly years from today.
Large temperature swings also can be problematic. As you cool anything it shrinks and as you heat anything it expands. Since a propellant is an inhomogeneous composite, different components expand and contract with different rates and large cyclic temperature swings can cause mechanical debonding if the various components in the propellant grain and possibly the casting tube from the propellant grain. High temperature can also cause certain chemical additives to migrate through the propellant grain. For example, in larger motors a bonding agent (rubber) might be used to coat the inside of a motor liner or casting tube. This rubber layer does not have any oxidizer or other additives in it so it will not oxidize. If the propellant grain is stored for very long time periods at very high temperatures, some components in the actual propellant can migrate by diffusion into this bonding layer and chemically change the properties.
In the US we do not normally have to store APCP propellant in a magazine as most APCP motors are not regulated. They still should be stored safely away from flame and in a secure location so they can be taken by an unauthorized person. Storing motors in an airtight container in the original packaging is recommended if you have a container of indicating
silica gel to remove the water vapor from the air. You can get bulk indicating silica gel pellets from a florist supply house (used to dry flowers) or
McMaster. You can purchase a premade container or make your own by taking a larger Tupperware container and filling it with indicating silica gel (1 pound or more), cover the top with nylon screening or cheesecloth, and use a Tupperware top with the center cut out to hold the screening in place. Place this inside your air-tight storage container and it will keep the air inside free of water vapor.
The silica gel has an infinite lifetime if you periodically regenerate it. Take a cookie sheet covered with baking paper and spread the silica gel pellets over it. Place the sheet in an oven at 250 F and keep it there for 12 hours (overnight). The indicating silica gel will go from a dull pink color to a brilliant iridescent blue when it is dry. Remove from the oven, and refill you container and put it back inside your air tight motor box.
As for the storage temperature. Look at the stuff in you medicine cabinet. Most drugs are stored near room temperature with temperature extremes not to exceed 50 F to 100F. Motors aren't that critical. For the most part, 35 F to 120 F should be ok for shorter times. If you go to a launch for a day and they get hotter or colder, I wouldn't worry, but I would try to keep them near room temperature or cooler.
FWIW.
Bob
