Many modern powders are advertised as being temperature insensitive -- meaning pressures and velocity will remain consistent over a wide temperature range.

However, there have been reports of African hunters loading their cartridges in cool weather at home, then, once they get into the 100+ degree heat of the African plains, they experience over-pressure conditions that make their ammunition unsafe. This has been extensively documented over the years. But we've yet to find much information regarding the opposite -- functionality in extremely cold weather.

We decided to run a test over several months to see what effect extreme cold has on some popular cartridges and powders

We selected the .44 magnum and the .375 H&H magnum as our test cartridges. They both use large amounts of fairly slow powders which should maximize the effect of the cold.

We selected two powders per cartridge. The first, a standard powder that has been around for decades that’s made with traditional technology. The second, a modern powder advertised to be temperature insensitive.

Specifically for the .44 Magnum we used Hodgdon H110 and Vihtavuori N110.

For the .375 H&H we used IMR 4350 and Hodgdon H-4350 (recent production).

Our plan was to run an initial test to see what the effects might be. Then, if we found significant variations between shots fired in +70 degree (Fahrenheit) weather and minus 40 degree weather, we would run a more detailed set of tests in the future. This project took many months as it required both a +70 degree day and a minus 40 degree day to test on.

We loaded 10 rounds of each powder -- five of each, to be fired in nominal +70 degree weather and the rest to be fired at a minimum of -40 degrees Fahrenheit, if not colder.

For the .44 Magnum we used Hornady 265-grain, jacketed soft point bullets.

For the .375 H&H, we used Sierra 300-grain, boat tail bullets.

CCI Magnum primers were used in all cases.

All of the rounds were hand weighed on a digital scale and cases selected for near identical weight and volume.

We fired the warm weather test in April of 2011. Recently, a couple of us had the opportunity to travel to a location with  -40 degree weather and so we fired the remainder.

In the warm weather tests we fired a single shot and allowed a 15 minute cool down time to try and keep the temperatures near a constant 70 degrees both for the weapons and the cartridges. Both the test weapons and cartridges were kept as close to 70 degrees as possible for 10 hours before the test to ensure test reliability.

The cold weather tests were also fired single shot but only 5 minutes was allowed between shots. Actual test temperature was -41 degrees which allowed the weapons  to cool down much faster . Both weapons and cartridges were kept at ambient air temperature ranging between -35 and -43 for 12 hours before testing.

.44 Magnum:

.375 H&H:

When shooting the .44 magnum with H110 under the 40 below conditions, not only were the velocities erratic but there was a noticeable delay between the hammer falling and the gun firing. These results clearly show that H110 is not a cold weather powder and can even be quite dangerous to use, due to the hangfires that resulted. We wish we had more rounds to test with. But at -40 the desire to stay outside any longer than necessary was not very great.

All the other loads performed well. The IMR 4350 lost a little velocity but was consistent and ignition was not a problem. H4350 and N110 proved themselves to be very stable at low temperatures and would probably be the powders to use under such conditions.

We’re planning a more detailed test with a wider range of cartridges and powders.  It may take a year so so to complete but will provide even more data on this unique phenomenon.