Bill's second guess is right. Some people believe that a warm gun in cold weather shoots tighter. I can't prove it or disprove it.
Ok I have to cry fowl. I knew what it was right off the bat. I've played with magnum rifles for years. I used to be a reloading nut. Someone way smarter than me came up with trajectory charts based on muzzle velocity, bullistic coefficents, altitude and wind speed. I can put a few numbers in my laptop and know where a bullet is at 2000 yards.
Shoot a mag rifle and I'm telling you the first shot doesn't count at 500 yards. Once the barrel is warm it will shoot straight until the barrel is hot enough to burn you. Guys at the range thought I was crazy. But I'd bring bags of ice to put on my barrel to keep it cold enough for a good first shot.
My longest successful shot ever was 796 yards on a mule deer in WY. The first long range kill I made was 500 yards. I've never killed a good buck that far away, but back then the shot was more important than the antlers. There is nothing quite like sqeazing the trigger and having your rifle settle back down on the rest in time to see your bullet hit the target.
I tell all the 20 year old hunters I know to head west now! When thier young.
I'm not in the same shape as I once was. But in my early 30's the mountains of Colorado and Wyoming where magical.
Today I shoot factory loads at deer just out of bow range.
Native,
There some pretty custom guns. As a teenager I shot against some custom German Anshutz .22 calibers.
With my borrowed customized Winchester model 52 and it held its own. :)