Thanks.
My experience is that the temperature of the rifle does affect velocity. I have tested ammo both ways, by heating.cooling the ammo only, and by firing in outdoor conditions from below zero to 100F, with the ammo often heated a little more by "greenhousing" it in a clear plastic bag. Sometimes frozen ammo works about like it does in actual cold, but more often it doesn't.
This would require quite a bit of explanation before I'd buy it. The working theory is that powder burns differently depending on its start temperature. Possibly the primer explodes differently too. If changing the temp of the rifle chamber or barrel mattered, an entirely new physical theory of what's happening would be required and not much is coming to mind. Maybe the bore contracting in the cold?!? I did a little math on that, and I believe going from the hottest to the coldest possible "cold bore" barrel temp only changes the bore diameter a couple ten thousandths, so that's hard to believe.
I'm not saying it's not interesting, but absent a physical theory of what's going on I suspect error/testing difficulties.
Our smokeless powder are progressive powders, which means they burn faster and hotter at higher pressures, which promotes even higher pressure.
Yet there is only a finite amount of energy in a powder charge. A certain part of which goes to heat barrel steel. More energy is consumed by cold steel than by warm steel. And the loss of energy to cold steel slows the progressive nature of the powder burn.
That is the theory of the mechanism by which a cold barrel reduces chamber pressure and muzzle velocity. Denton has shared with us on a couple of occasions data derived from actual shooting which supports such theory.
Personally, I have seen approximately 250 fps difference between the first shot from a cold bore and the third shot as the barrel heats in a 26 inch Model 70 Classic sporter in 264 using 140 gr partitions in combination with RL 25 (early production). The fast loads were accompanied by blown primers and case heads expanded so much they would not fit into the shellholder on the reloading press.
I recorded, the same data on two different days with this load. Shot #1 safe and sane at near 3100 fps, second hitting 3200 fps, and third exceeding 3300 fps.
