Don’t Overheat Your Ammo in Hot Summer Months
Summer Solstice 2020 was June 20th, and July’s nearly here. That means “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.” |
To learn more about how ambient temperature (and primer choice) affect pressures (and hence velocities) you should read the article This Editor had the personal experience of 6mmBR hand-loaded ammo that was allowed to sit in the hot sun for 45 minutes while steel targets were reset. The brass became quite warm to the touch, meaning the casings were well over 120° on the outside. When I then shot this ammo, the bullets impacted well high at 600 yards (compared to earlier in the day). Using a Magnetospeed, I then chron-tested the sun-heated ammo. The hot ammo’s velocity FPS had increased very significantly — all because I had left the ammo out in the hot sun uncovered for 3/4 of an hour.
Powder Heat Sensitivity Comparison Test
Our friend Cal Zant of the Precision Rifle Blog recently published a fascinating comparison test of four powders: Hodgdon H4350, Hodgdon Varget, IMR 4451, and IMR 4166. The first two are Hodgdon Extreme powders, while the latter two are part of IMR’s Enduron line of propellants.
The testers measured the velocity of the powders over a wide temperature range, from 25° F to 140° F. Hodgdon H4350 proved to be the most temp stable of the four powders tested.
Similar Posts:
- Don’t Roast Your Ammo — Watch Temps in Hot Summer Months
- Smarter Shooter: Keep Your Ammo Cool on Hot Summer Days
- Beat the Heat: Keep Your Ammo Cool in Summer
- Tech Tip: Keep Your Ammo Cool this Summer
- Beat the Heat — Keep Ammo Cool During Hot Summer Days
Tags: Cal Zant, Enduron Powders, H4350, Heat, July Temperature, Powder Heat Sensitivity, Precision Rifle Blog, Varget
I live in Australia where heat and mirage are major problems in summer.
An Australian bullet maker has come up with a powder that is affected minimally by heat. Worth having a look at.
Heat is one thing. Humidity is what kills me.
I’ll take 105-f dry heat over 85-f with 95+% humidity any day.