June is when many handloading hunters start thinking about working up a new load for big game, and sighting-in their rifles for seasons which start as early as August, whether pronghorns in New Mexico or caribou Up North. However, there’s one potential problem with this early preparation–the wide variety of temperatures that might be encountered.
I’ve encountered many hunters who think temperature resistant rifle powders are another form of hype to sell us more stuff, because they’re never “seen” temperature make any difference in their hunting. This certainly can happen, depending on the not just range of temperatures in their area, but the typical range of their shots. Temp-resistance isn’t going to make any significant difference, for instance, when hunting whitetail deer from stands at typical “woods” ranges, which rarely exceed 100 yards.
But it can at longer ranges, even only 200 yards. This is described in Chapter 10 of The Big Book of Gun Gack II, “Temperature and Rifle Powder,” when I took a mule deer doe at around 200 yards on a cold November day in the early 1990s.
Since the major point of doe-hunting is venison, I aimed behind the shoulder to ruin as little meat as possible—but the bullet landed in the middle of the shoulder. This seemed odd, especially since I shot from prone with a very accurate .270 Winchester, and had long ago lost any trace of “doe fever.”
So I range-tested the load on a cold morning when the temperature was right around zero Fahrenheit, both by shooting at a 100-yard target from a benchrest, and chronographing the load. At the time we lived in a country house on seven acres, so the chronograph was kept warm in the house until the shooting, while the rifle and ammo were kept in our barn overnight to chill—as they would be when hunting.
The group landed three inches to the right of where it did when sighting-in during early October, and the velocity was around 130 fps slower. I then waited for a warmer day and retested the rifle and load. It went back to shooting right where I’d sighted-in earlier in the fall—and velocity was also “normal.”
That cold-test took place in January of 1991, and I’ve repeated the same test with numerous rifles, cartridges and powders since then. I also eventually started testing on hot days, since a lot of hunting takes place in warmer-than-average temperatures, whether prairie dogs, big game in late summer in North America, or other places in the world, especially Africa. When I travel to hunt I take along a small thermometer, among other measuring tools, and when hunting the Selous Game Reserve in eastern Tanzania in 2011 I showed midday highs consistently above 100—and since the hunt took place in the southern hemisphere’s springtime, temperatures kept rising during the 18-day hunt. I finally started leaving the thermometer in camp, because I didn’t want to know how it was!
In our part of Montana, daytime highs rarely hit 100, so sometimes the ammo was either heated up a little more by putting it inside a clear Ziploc bag with that small thermometer, or shooting the rifle repeatedly to heat up the barrel—common in prairie dog shooting.
Eventually several trends appeared. First, just about any modern smokeless rifle powder will show little variation in velocity (and hence point-of-impact) at Fahrenheit temperatures from the 20s to the 70s. But both above and below that range problems can occur.
I also found that newer temperature-resistant rifle powders result in consistent velocities and hence point-of-impact down to below zero—but even they will gain some velocity and perhaps change point-of-impact above 80 degrees. However, they gain less “hot” velocity than many popular standard powders.
The specific rifle and barrel can also affect point-of-impact. Heavier-contour barrels show less variation, as do some rifles with lighter-contour barrels firmly bedded in the forend. This is especially true of Ultra Light Arms rifles, with their very stiff synthetic stocks. All of this is described in much more detail in in Gun Gack II, which also includes a list of various handloads tested at different temperatures in rifles chambered for cartridges from the .17 Hornady Hornet to .375 H&H.
Luckily, more powders are becoming more temp-resistant these days.
The first I encountered were the Hodgdon Extremes made in Australia, which appeared in the U.S. in the 1990s, but today several other companies offer them, including Alliant (www.alliantpowder.com) and Vihtavuori (www.vihtavuori.com) which in the past few years has made all their powders temp-resistant, and added a decoppering agent as well. There are also some powders not advertised as temp-resistant that do very well, especially Ramshot Big Game, one reason it’s used in more of our hunting handloads than any other powder. (Ramshot powders have been distributed and sold by Hodgdon for a couple years now.)