Tech Tip: Keep Your Ammo Cool this Summer
Well folks, it’s almost July — the means we’re moving into “peak heat” summer conditions. It’s vitally important to keep your ammo at “normal” temps during the hot summer months. Even if you use “temp-insensitive” powders, studies suggest that pressures can still rise dramatically when the entire cartridge gets hot, possibly because of primer heating. It’s smart to keep your loaded ammo in an insulated storage unit, possibly with a Blue Ice Cool Pak if you expect it to get quite hot. Don’t leave your ammo in the car or truck — temps can exceed 140° in a vehicle parked in the sun.
For example, barrel temperature was a key factor: “Both barrel temperature and powder temperature are important variables, and they are not the same variable. If you fail to take barrel temperature into account while doing pressure testing, your test results will be very significantly affected. The effect of barrel temperature is around 204 PSI per F° for the Varget load. If you’re not controlling barrel temperature, you about as well might not bother controlling powder temperature, either. In the cases investigated, barrel temperature is a much stronger variable than powder temperature.”
Temp Strips allow shooters to monitor their barrel temperature. Excessive barrel heat can raise load pressures as well as shorten barrel life! |
To learn more about how ambient temperature (and primer choice) affect pressures (and hence velocities) you should read the article 
And so, on that last box’s comments: if you are the type shooter that often finds the need to shoot repeatedly for several rounds in a row, you are best to consider VERY carefully any need you have to load those rounds at maximum pressure in what is usually SLOW fire testing.
The McMaster-Carr temp strips are at https://www.mcmaster.com/#temperature-strips/=1dhhbbe
If you are not familiar with McMaster-Carr, check them out. A fantastic resource.