ammo exposure to extreme heat/ temperature changes


piece of meat
June 28, 2012, 01:44 PM
Are bullets affected at all by sitting all day in a car in which the temperature is over 110 degrees? How about, say, loaded magazines going from being indoors at a temp of 60ish degrees all night immediately being transferred to a ridiculously hot car all day long?

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June 28, 2012, 02:22 PM

Military's couldn't fight wars in the middle-east, cops couldn't go about armed in Arizona, and I couldn't shoot in Kansas this summer if 110 degrees had any effect at all.

Going from A/C cold indoors to car hot outdoors has no effect either.

Going from cold winter outdoors to heated indoors will produce condensation on cold metal and cause your gun & mags to rust if not properly dried & protected.
But it won't hurt the ammo.


June 28, 2012, 02:49 PM
All true!

June 28, 2012, 02:55 PM
This spring I found some ammo I reloaded back in 1994. For the last twelve years it was stored in a shed where summer temperatures consistently get over 100 and winter temps get well below freezing (Moab, Utah). It shot fine.

Old Dog Man
June 28, 2012, 02:56 PM
The only time I've had any effect on temp. effecting ammo was going from sea level sight-in to -30 F was a change in point of impact of 2" lower and not same group size. However that's extreme enviroment change, which I expect is normal. Al

June 28, 2012, 03:10 PM
Are you worried about bullets or cartridges?

Condensation going from cold to warm has been mentioned, externally lubricated ammunition (.22lr/l/s is about the only common/current externally lubed bullets) can lose the lube or have it melt and re-form in clumps that will cause buildup in the gun when fired or failures to feed from the magazine.

I would replace ammunition that rode around in a car more frequently, the warm/cold and-or the vibration might make the powder a much finer grind and change the burn rates given enough time ... not a major concern, just change it out every few range trips.

June 28, 2012, 04:58 PM
Lots of reloaders tumble live rounds with no problem... there is no amount of vibration from riding around in your car that is going to do anything to the powder.

June 28, 2012, 05:08 PM
True too!

Vibration in a car will not grind up the powder or change the burn rate.

Again, military ammo gets a workout 1000 times greater riding around in 10,000 mile cargo shipments, and riding in Hum-V's and helicopters.

Now thats vibration!
And it doesn't hurt the ammo one bit.


June 28, 2012, 05:20 PM

Temperature effects a cartridges chamber pressure and some powders are more tolerant than others. Military specs. call for use of powders that are less temperature sensitive than many commonly used in non-military rounds. But being less sensitive still means there will be changes, just not as much.

In extreme heat a cartridge will generate more pressure when fired, with resulting greater velocity. In extreme cold you will generate much less pressure and velocity. With many rifle rounds you are looking at around 1 fps for each degree of temperature change.

Ammo sitting in a hot car could easily reach 150-160 degrees and generate an additional 100 fps or so of velocity than it would at 50-60 degrees. If you are looking at a load that is already close to a max charge it could be enough to create an overpressure load.

In extreme cold, say -40 the load could easily be 150 fps slower than when fired at 70 degrees resulting in long range shooting errors. MIlitary snipers consider temperature and its effects on their trajectory before attempting long shots.

This is only a problem if the ammo is fired when it is hot, or cold. The ammo is not ruined and will perform normally when allowed to come back to normal temperatures.

June 28, 2012, 05:54 PM
I found some ammo in a unheated storage building that was from the 1950s back in 1998 and it all shot fine. We found 3 boxes of 22 ammo, Long, Short and LR and some 16 gauge shotgun shells 1 box paper hulled the other early plastic.

Eastern Arkansas is sub-topic to the White River freezing over weather.

PBR Streetgang
June 28, 2012, 05:59 PM
Ding! Ding! Ding! jmr40 wins the prize!!!!!!!!!

higher temps= higher pressures

June 28, 2012, 06:02 PM
If I remember the temperature correctly, at about 135 F the nitroglycerin in double based powders turns to vapor, and when the temperature drops, it condenses out. When this happens, the distribution of NG in the powder will be very non-uniform and the cartridges will become less uniform.

June 29, 2012, 07:19 AM
Yes, but is designed to be able to handle it. They know it may be shot in high temps. Here in Alabama, I get to test any max loads I have in near 100 degree temps. I shot two .223 loads over the chrono in 102 temp yesterday with everything sitting in the car all day and then set out in the sun for a few minutes before shooting to check them. One needs to back off a hair. It was perfectly fine in 90 degree temps. The other load was fine.

June 29, 2012, 12:56 PM
I used to be involved in ordnance testing back in the 1980's where we were required to temperature cycle our devices from -40 to +165f. "Accelerated Aging": ten cycles a day, 24 hrs a day for 2 weeks as I recall. The chambers had an oven above and a freezer below with an elevator to present the test items to the required environment.
Few of the propellants we used were off-the-shelf although we did use Bullseye and Unique in a few devices. Anyway, the vast majority of the propellants were either single or double base purchased from the same propellant houses that made commercial rifle and pistol propellants: Alliant, Hodgdens, Accurate Arms, etc.
After environment testing the devices were fired and a pressure/time trace recorded for each test to be compared with data from devices that had not been subjected to such testing.
Qualified devices showed no effect from these environmental tests.
Incidentally, in regard to the comments above; when fired at -40f some propellants showed HIGHER peak pressure than at ambient which the chemical guys attributed to fracture of the propellant grains resulting in more surface area of the grains. This didn't happen until extremely low temperatures were used so, unless you plan on shooting at -40f, it's nothing for the average shooter to worry about (and very little to worry about even if you do).

piece of meat
June 30, 2012, 12:26 AM
Thanks for the good replies!

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