TargetTalk

Will heat affect ammo? We recently purchased a trailer for the club equipment and I have been leaving the ammo in it as well. Lately a few of the better shooters have been having some really bad fliers. I had been blameing it on their positions or lack of checking NPA. But after a few insisted that it wasn't them, we put one on the bench and got the same results. Never had this problem with the ammo before. Not saying that it is the best but always pretty good.

I have always been told that storing ammo in the heat was bad for it and would cause the ammo to have fliers etc. I have never taken the time to actually think about why excessive heat would damage ammo or do any research before. Instead I figure better safe than sorry, and I keep my ammo out of the heat.

Brian

Heat will absolutely affect ammo. Hot enough heat will start to melt the wax on the outside of the bullet. I had teammates who went down to Ft. Benning, Georgia, and let their tenex get hot enough to melt the wax. The results were awful. I would recommend storing ammo in a cooler. I have a small one I carry around. I don't put any ice in it or anything like that, but a cooler will be affected less by the heat. Had a coach recommend me this years ago.

when at a competition i always set my ammo in the shade while many people leave it in the sun. :)

Depends on the level of heat. The late great Bert Brookes at Eley did a number of interesting experiments, including laying a batch of ammo and a barrel up for 5 years to see if the group changed just as a result of "ageing". He also posted ammo to the US via air mail, and had a friend send it back to see if pressure changes affected it. Turns out ammo is pretty resiliant and it takes a lot to degrade it.

Heat is one of the big things that can do it though. I've got a box of Eley .22 ammo that was left in the sun, and the wax ran down to form a blob on the tip (it was hanging nose-down in the 50-round racks you get in Eley boxes). That can also happen over time, depending on the storage conditions.
Biathlon shooters will tell you that what works well at room temperature may not even fire on a Biathlon range in the cold, and the same is no doubt true of high temperatures as well. It'll fire, but probably won't behave the same. You wouldn't want to be putting it in a chiller cabinet, but equally, keeping it out of direct sunlight is a good idea. A cooler box keeping it at maybe 20 degrees (normal room temperature) is ideal if you're out somewhere hot.

Bear in mind Eley (for instance) is made in the UK, where the ambient temperatures generally range from 0-25 celsius, and is used widely in temperate Europe. If you leave it in a hot trailer on a sunny day in Arizona, where temperatures are creeping north of 40-50 celsius in the shade, you're well outside the normal manufacturing, testing and operating conditions for the ammo!

The other thing to consider is whether the heat is affecting the rifle itself. If the barrel is warming up, the metal will be expanding, which could change the bore very slightly. It could also affect the bedding bolts and the slight expansion they would undergo might affect the torque and tightness to which the action is bedded in (I don't have anything quantifiable, just suggesting it as things that probably happen, even if only to a negligible and unnoticeable degree!).

There has been studies done in the past that shows that heat can affect the chemical makeup of the powder. For example some of the older powder if stored in hot conditions on a long term basis will cause a chemical breakdown of the powder. For example the powder used by the Battleship Iowa when their was an explosion in one of it's gun turrent's was stored in a barrage on the Mississippi and investigations found that chemicals in the powder had broken down to the point that the powder was very unstable. The newer powders by the manufactures claim to be more resistant to heat, but I have seen some rounds that had been sitting in a hot car and the rounds would shot like it was a hot load.

As a rule metals oxidize faster when subject to heat and humidity. A trailer that is closed and has some moisture inside it (all do) will accelerate the oxidization. I have little doubt that the lead oxide will have a detrimental effect on the ammo.

"Cool-dry" would be better. But don't put ammo in the refrigerator because when you take it out moisture will condense on the ammo--also not good.