Q: I live in rural upstate New York, and summer temperatures reach in excess of 90° F—with car and attic temperatures exceeding triple digits. Is there a known “maximum safe temperature” for the storage of ammunition? What would be the ideal conditions to store ammunition?
A: Nitrocellulose, the primary ingredient in smokeless powder, is hygroscopic, which means it absorbs water from the air that can affect both shelf life and burn rate. Coatings and stabilizers, such as methyl and ethyl centralite, are added to prevent this. Unfortunately, the effectiveness of these compounds is reduced as the temperature rises.
The standard advice is to store ammunition in a “cool, dry place.” Manufacturers try to store powders at 70° F +/- 5 degrees. For handloaders, the best advice is to store powder in a cool basement or an interior room that is of “comfortable” temperature.
—Charles E. Petty