Thermal Effects on Point of Impact

The first shot from a cold, clean barrel often lands differently from subsequent shots. The combination of residual bore solvent, barrel metal temperature, and unlubricated surface creates a slightly different launch condition for that first round.

Cold bore deviation on a precision rifle ranges from zero to over 1 MOA depending on the barrel, load, and how the rifle was cleaned. Know yours: at your next range trip, fire the first shot from cold and mark it separately. Fire your group and note the delta. Some shooters intentionally foul the bore with one round and discard it before a cold bore shot that matters.

Propellant burn rate is temperature-dependent. In cold conditions (below 30–40°F) powder burns more slowly — muzzle velocity drops, trajectory becomes more curved, and you hit low. In hot conditions (above 90°F) powder burns faster — MV rises, you hit high.

The effect varies with powder formulation. Hodgdon Extreme series powders (H4350, Varget, H4831SC) are specifically engineered for temperature stability — typically less than 25 fps variation across 60°F of temperature change. Ball (spherical) powders are generally more temperature-sensitive. For a rifle used across seasons, temperature-stable powder is worth the premium.

Rule of thumb for non-TS powders: expect ~1 fps per °F of temperature change. 50°F temperature swing = ~50 fps velocity change. At 500 yards, 50 fps means roughly 0.5 MOA of vertical shift.

As the barrel heats from repeated firing, its steel expands and the harmonic vibration frequency shifts. For most semi-heavy and heavy-contour barrels, the practical effect is a gradual upward POI drift over a string of fire — typically a few tenths of MOA over 5–10 shots. Pencil-thin sporter barrels are dramatically worse.

If you notice groups walking upward during a long string, barrel temperature is the likely cause. Let it cool. Tactical competition stages, where you must shoot 10+ rounds without cooling, are explicitly designed to test this; practice under those conditions if they apply to you.

Note the ambient temperature when you confirm zero and when you shoot DOPE data. Record it in your range sessions. If you are shooting in conditions 30°F or more different from your zero conditions and have a temperature-sensitive load, fire one confirming round before trusting your DOPE.

For hunting: if you zeroed in summer heat and are hunting in freezing conditions, verify zero at hunting temperature — or hunt with a built-in mental adjustment. The difference can be 1–2 MOA of drop at 300 yards.

Going deeper: the Advanced Ballistics track's 'Density Altitude' lesson rolls temperature, pressure, humidity, and altitude into one number that captures all of this — the field shooter's master variable for how far the bullet drops on a given day.