Temperature changes affect everything in life, including shooting. The air is way more dense for one thing when it gets frigid, thus causing more aerodynamic drag on the bullet in all phases.
Pressure goes up I'm told in the barrel too, when it gets cold and bullet drag could also be increased with frigid temperatures.
As for bullets hitting high when cold, it could be because of the barrel time theory at work. The theory goes....:
When a bullet leaves the barrel, it travels at X velocity which equates to Y time in the barrel. The barrel imparts a muzzle lifting (muzzle flip) with each shot and if you have a bullet that stays in the barrel longer, it will exit at a higher point in the arc than will a bullet going faster.
Therefore, with your warmer bullet barrel time (faster), the bullet leaves the barrel at a lower point in the "flip". When it froze up, the bullet is going slower and therefore exiting at a higher point in the muzzle flip (arc) and is therefore hitting the target at a higher point of impact.
If you have screwed your barrel to a heavy table that allows for sliding back of the rifle on bearings etc, this probably wont work in theory and your bullets will hit low.
Aloha... Tom
