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From time to time, I've heard this subject mentioned and the opinion expressed is almost always that heat changes the chemical composition of the powder and makes it dangerous. What I'm thinking of is keeping some spare ammo in the trunk of my car 24/7. Heat around here can get up to 105 deg and ? how much more in the direct sun.

The only experience I've had was when a fella at the range was showing off his car gun - a Rem 870 that he kept in his trunk along with the shells. He let me shoot it (it had a diverter on the muzzle) and that thing literally rattled my teeth! Wasn't the gun but the ammo, I think.

So, how do police officers carry ammo in their trunks safely all day? How about the army who probably stores their ammo under a tarp in Iraq?

Maybe this isn't something to be concerned about but I'm really curious.

Thanks

RIKA :)
 

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After time constant heat can cause a break down of the propellant. You could end up with erratic ignition, decreased accuracy and excessive pressures. Rotate your ammo every 30-60 days.
 

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As Garand says, after time, powder can break down.

Of more immediate concern is the temperature of the ammunition at the time it is fired. Some powders are relatively unaffected by temperature, as are most primers, but some powders are sensitive. Blue Dot gives erratic performance when it is cold, low velocities and sometimes noticable delays in ignition. Red Dot will give very high pressures when it is hot. Several others are also sensitive, those two are just the worst I've come across. Hodgdon has some powders they advertise as being temperature insensitive.

DC
 

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In rifle cartridges, the effect is more pronounced. Keep your ammo out of the sun for the most part when shooting. If it gets hot, it will shoot differently and hotter.

Mike
 

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Raider

What the heat is effecting is the powder and the pressures it produces upon ignition.

When the pressure goes up, at the least, the point of impact changes so your come-ups change. Highpower shooters, who are working at a level of precision not obtainable in the field, keep thier ammo in those soft six-pack coolers. They are trying to squeeze out everylast varitable. If you are running on the high raggety edge of the pressure curve, it can cause you high pressure problems. I see it all the time, with the guys that are using 748 in thier AR's in Service Rifle Matches. As a rule, I stay away from ball powders.

The best bet though is to use powders that aren't temp sensitive in the first place. I load my .308 M118LR equivelent load with Varget powder. 46 grains even, in Fed Gold Metal Match brass puts me right at 2800 fps with Sierra 175 grain Match Kings with a deviation of about 12 with my OAL. Note though, that my OAL is long, as my rifle is chambered with a reamer that allows seating the bullet out a bit and my box magazine has been modified to run the longer rounds. The load is very stable at high and low temps so my zeros always work. I go though kegs of Varget it works great in both 5.56 and 7.62.

Teuf,
 
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If you are not talking about match shooting, but combat and SD, even with a hot summer, ammo can last a long time and still be usable. I've had .308 ammo in a barn for 10 years, shot it out of a M1A and it still grouped 2 inches at 100 yards. And that was reloads, not sealed military ammo.

Yes, do rotate ammo, that is shoot it up, over time. But unless you are into match shooting it is not so important.

If you are not keeping it in a car trunk all summer, every summer, then it should shoot fine. What I do with my AR is I keep a bandlero in the truck with my AR. Every year I shoot that ammo up and replace it with freash ammo. The freash ammo does not have to be brand new, just kept in a cool place.
 
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