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Temperature Fluctuations And Reloading Brass-Part 2


If you haven’t read part one of this article, it is suggested you go ahead and do so now.

With frozen-ammo velocities in the bag, I then shot the ammo still cooking on the dashboard of my pickup. The cartridges were hot to the point of being uncomfortable to hold.

The result? The answer to the first of our threefold question is yes: Temperature extremes do affect velocity. Both propellant types shot significantly higher velocities with the hot ammunition.

The answer to the second question is also yes: The disparity was much less with one propellant brand/type than with the other. Specifically, H-1000 had 44 fps disparity between temperature extremes; RL-22 had 130 fps disparity. The difference between propellant types — 86 fps — was significant.

Here’s a breakdown of the results with each gunpowder type:

Hodgdon H-1000 Frozen Hot Difference
Velocity (fps) 2,892 2,936 44
Extreme Spread 70 12
Standard Deviation 25 5

Alliant RL-22 Frozen Hot Difference
Velocity (fps) 2,972 3,102 130
Extreme Spread 34 6
Standard Deviation 14 2

As an aside, an effect I didn’t foresee was that hot ammunition — at least in this case — is more consistent than cold ammo. Take note of the far tighter extreme spreads and standard deviations.

To answer the last of our threefold question (is temperature-induced variation enough to cause a miss at hunting ranges) we need to run some ballistic calculations. Keeping things very simple, I used the calculator on Hornady’s website and plugged in the appropriate numbers. Here’s what I found:

With RL-22 powder and a 200-yard zero, the 160-grain Nosler AccuBond (B.C. .531) will drop 18.8 inches at 400 yards with the frozen ammo and 17.1 inches with the hot ammo. The difference is less than two inches. With H-1000 the difference is less than one inch. So the answer is no: When using a temperature-sensitive propellant, even extreme swings in temperature won’t cause enough disparity in point of impact to make us miss a game animal.

How about for long-range shooters that really stretch the distance? Let’s double the distance and run the numbers:

Again with RL-22, the projectile drops 144.5 inches with the frozen ammo and 131.2 inches with the hot ammo. The difference is 13.3 inches, which is certainly enough to cause a complete miss on a deer-size animal, and a miss — or worse, a wound — on an elk-size animal. Clearly, as distances stretch, temperature sensitivity becomes far more critical.

Let’s look at H-1000: At 800 yards, the bullet drops 153.8 inches with the frozen ammo and 148.6 inches with the hot ammo. The difference is much less, only 5.2 inches. Depending on the size of the game, that’s still enough to potentially cause a miss, but the disparity is more acceptable.

We don’t have space to address it here, but another element that exerts additional drag and drop on cold ammunition is the density of colder air. Lower temperatures result in more drag on your bullet, which will open up the disparities shown above even more.

The multifaceted nature of this “fact or fiction” topic bars a simple yes or no answer, but we can come away with this:

Yes, temperature does affect velocity, and it affects some propellants more than others.

However, within common hunting distances out to 400 yards or so, the disparities are little enough that we don’t need to worry about them.

If you shoot long range, though, you’d better be familiar with your velocities and the trajectory of your bullet in the conditions in which you’ll likely shoot. If you hunt in very cold weather, get out and practice in very cold weather. Leave your rifle and ammunition out to freeze overnight, and chronograph your ammunition. Then plug those numbers into your ballistic app.

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