Home Forums Hunting & Shooting Ask The Gunwriters Bullet Velocity and Barrel Temps

Shooting a 6.5-300 Wby with bullets flying out at near 3,500 fps next to my Labradar, the velocities seemed to gradually increase as the barrel got hotter. Is that a coincidence or something else?

Not coincidence.

Some powders are temperature compensated, but usually only for a single cartridge. For example, Varget is very temperature stable in the 308, but very unstable in the 223.

For powders not particularly well matched to their cartridge, or for powders that have no temperature compensation, the temperature of the powder almost does not matter. Nor does ambient temperature.

What matters is the temperature of the barrel, and the temperature of the brass and the metal in the projectile. Ambient temperature only matters because it influences these.

The mechanism is that the rate of transfer of heat energy between two bodies is proportional to their temperature difference. Cold steel, brass, and lead rob more heat energy from the propellant gas than hot ones do.

Interesting. Thanks for taking the time to provide that info, Denton.

Not sure what kind of increases you were seeing but I'll just drop this is a note kind of unrelated Maybe. Battery operated chronograph I have seen as the battery loses voltage the readings will climb until they abnormally High. I have no idea if that would affect the labradar in the same way.