Keep your ammunition cool in summer

Today, 2024, is the Summer Solstice. It’s the longest day of year. Right now, the Northeast USA is experiencing a major heatwave. This means that summer’s “peak heat” conditions are already here. It is vital to keep your ammunition at “normal” temperatures during the hot summer months. Even if you are using “temp-insensitive powders”, studies show that pressures can rise dramatically when cartridges get hot. This could be due to primer heating. Keep your loaded ammo inside an insulated unit. You can even use a Blue Ice Cool Pak to help cool it down if you think that the ammo will get very hot. Ammo can reach temperatures of 140 degrees in a car or truck parked in direct sunlight. Denton Bramwell’s study Pressure Factors, How Temperature Powder and Primer Affects Pressure, covered the way ambient temperatures, barrel warming, and powder heating can affect cartridge pressures and hence velocities. In the article, Denton Bramwell used a pressure-trace instrument to analyze temperature’s effect on ammo performance. Bramwell’s experiments produced some fascinating results. The barrel temperature, for example, was a major factor. Your test results will be significantly affected if you fail to consider barrel temperature when performing pressure testing. The Varget load is affected by barrel temperature at around 204 PSI/Fdeg. If you don’t control barrel temperature, it is likely that you won’t bother to control powder temperature either. In the cases investigated barrel temperature was a stronger variable than powder temperatures. This Editor’s personal experience was with 6mmBR hand-loaded ammunition that sat in the hot sun while steel targets were being reset. The brass was quite warm, indicating that the casings had a temperature of over 120deg. The bullets were impacted high at 600 yards when I shot this ammo (compared to earlier that day). I then chron tested the ammo that had been heated in the sun using a Magnetospeed. The velocity FPS of the hot ammo had increased significantly, all because I left it out in the hot sunshine uncovered for about 3/4 of an hour. LESSON: Keep your ammo cool! Keep ammo under shade, preferably in a container that is insulated or under cover. You can use an ICE pack that is SEALED inside the container. We do not recommend H20 ice. Don’t use the container for both food and drinks. Powder Heat Sensitivity Test Cal Zant, of the Precision Rifle Blog, has published an interesting comparison test of four powders, Hodgdon H4350 (Hodgdon Varget), IMR 4451 (IMR 4166), and Hodgdon Varget (H4350). The first two powders are Hodgdon Extreme, while the last two are from IMR’s Enduron propellant line. Click here to view the full powder test results >> The testers measured velocity of the powders across a wide range of temperatures, from 25deg F up to 140deg F. Of the four powders that were tested, Hodgdon’s H4350 was the most temperature stable. [NOTE: New Alliant ReloderTM TS 15.5 also proved to be very temperature stable in AccurateShooter’s range tests.]