Guides · Air

Temperature: The Air and the Powder Are Two Different Problems

Cold air and cold powder both make you dial more, for different reasons. We split the two on 20°F and 90°F days for a 6.5 Creedmoor and a .308, and find the powder sensitivity at which the powder starts to outweigh the air.

5 min readSolved with the Ballista engineUpdated October 2026

On a 20°F morning a 6.5 Creedmoor that was zeroed on a 59°F day needs 0.72 mil more at 1,000 yd. Two separate things cause that. The cold air is denser, so drag is higher. The cold powder burns slower, so the bullet leaves the muzzle slower. They come from one thermometer reading, which is why they’re easy to lump together. They behave differently with range, and only one of them is a property of your ammunition.

Two effects from one thermometer

Air temperature changes density. At constant pressure, air gets denser as it cools. At 29.92 inHg the 59°F reference day has a density altitude of 0 ft. The 20°F day is at -2,690 ft and the 90°F day at 1,970 ft. Every rifle and every load feels this the same way, through drag. The density altitude article covers it in full.

Powder temperature changes muzzle velocity. Warm powder burns faster and builds more pressure, so the bullet leaves faster. Cold powder does the reverse. How much depends on the powder and the load. It’s usually given as a sensitivity in fps per °F, and it’s a property of your ammunition, not the day.

The sensitivity we assume, and why

We use 1.2 fps per °F for both rifles. It’s the value Ballista’s demo .308 profile carries, so the numbers here match what the app shows for that rifle. It is an assumption, not a measurement of any particular powder. At that rate the 20°F day costs 47 fps and the 90°F day adds 37 fps. If your load is more or less sensitive, the break-even table below tells you which side of the line you’re on.

Splitting the two on a cold and a hot day

We solved each day three times: cold or hot air with the powder held at 59°F, cold or hot powder in 59°F air, and both together as they’d really be when the ammunition has sat out in the weather.

Three things stand out.

The two effects push the same way. Cold air and cold powder both make the bullet drop more, and heat does the opposite for both. When the powder is at air temperature, they add. For the 6.5 at 1,000 yd on the 20°F day the air alone gives 0.31 mil and the powder alone 0.39, and together they give 0.72. That’s within 0.02 mil of the simple sum. The .308 needs 1.29 mil more in total, about 46 inches if you ignored the temperature.

The powder effect matters from the first yard. A slower bullet starts falling behind at the muzzle, so at short and middle range the velocity change is the bigger effect. At 600 yd on the 20°F day the powder costs the 6.5 0.19 mil and the air 0.08.

The air effect grows faster with range. Density works through drag, and drag has more time to act the farther you shoot. For the .308, which slows down more, the cold air overtakes the cold powder before 1,000 yd: 0.67 mil against 0.58.

Which one dominates for your load

Because the powder effect scales with sensitivity and the air effect doesn’t, there’s a sensitivity at which the two are equal. We found it by solving the 20°F day at sensitivities from 0.3 to 2.4 fps per °F.

At 300 yd almost any sensitive powder outweighs the air. At 1,000 yd the line sits at 1.0 fps per °F for the 6.5 and 1.4 for the .308. A load that changes less than that is mostly an air problem at long range. A load that changes more is mostly a powder problem everywhere.

Powder temperature isn’t always air temperature

The powder temperature that counts is the one at the moment of firing. Ammunition in a sunny truck, on a dark mat in the sun, or chambered in a hot barrel for a minute can sit well above the air. Rounds carried in a cold pack at dawn can sit below it. That’s when the two effects stop moving together, and a solver that ties powder to the air will be off by the powder part alone.

In Ballista each load has “Measured at” (the temperature you chronographed at) and “Temperature sensitivity” in fps per °F. A sensitivity of 0 means the load doesn’t change with heat or cold. On the Air sheet, “Powder at air temperature” is on by default. Turn it off and a “Powder temperature” field appears for ammunition that is warmer or colder than the air. The DOPE tab’s “Temperature chart” card prints elevation at 20, 40, 60, 80 and 100°F, with the powder following the air unless you’ve set its temperature apart.

Measuring and using your own sensitivity

1. Chronograph the same lot on a cold day and a warm day, as far apart in temperature as you can manage, with the ammunition left out long enough to reach air temperature. Sensitivity is the velocity difference divided by the temperature difference.
2. Enter the velocity with the temperature you measured it at. A muzzle velocity without its temperature is half a number.
3. Keep the ammunition at a known temperature: shaded, and out of a hot chamber until you’re ready to fire.
4. Expect the air effect to matter even with temperature-stable powder. At 1,000 yd the 20°F day costs the .308 0.67 mil from the air alone.