I love the cold. I don't see group size changing dramatically with temp, but the POI definitely does, especially at longer ranges. I see it really being 3 things.
1st barrels have a resonant frequency and the POI moves a lot with different loads or velocities. The worst I have ever seen for this is my 1898 Krag. If you load up a batch of loads with say, 40, 41, 42, 43, 44, 45 grains of powder, with all else being equal, the POI can change 12 inches at 100 yards in that range of charges. With certain bullets and powders the POI will go up with higher loads, and sometimes it goes down with higher loads. It depends on how the barrel is whipping at the moment the bullet leaves the bore. That is by far the most extreme example I've ever seen. The trick when dealing with that is you need to find the top or bottom of that harmonic window. I now test when I am working up a load to find a charger where the POI doesn't shift even if you reduce the powder load 2 or 3 grains. I am more concerned about making sure I'm on that node than finding the smallest group.
The next thing would be the bedding of the barrel and action, especially with wood stocks that are contact with the barrel. I glass bedded a ruger M77 for a family member that would changed POI several inches depending on the time of year. He was constantly chasing it around with the scope turrets and it would just never stay zero'd. After I floated the barrel and glass bedded the action the POI no longer wanders around. My father in law on the other hand has a weatherby with a full contact walnut stock and I don't think the scope caps have been off of it for 20 years.
Lastly, velocity can and will change dramatically with very cold temps, and just because a powder is advertised as temp insensitive there is no guarantee that it will work decently below 0. For example most ball powders I've tested are actually not bad when going from 50 degrees to -20. They seam to be more of a problem going from 50 to 100 with pressure spikes, but I don't see a huge difference going the other way in temperature, especially with a magnum primer.
As an example from my notes, I tested my 25-06 several years ago with two different loads. One load was with H4831sc which is regarded as one of the most temp stable powders ever made, and the other was with RL19, which is commonly known to be pretty temp sensitive. The load with H4831sc lost 350 FPS going from summer temps to -18 deg F! The load with RL19 only lost about 40 fps.
This last winter one of my projects was to find a temp stable load for my 444 marlin. I have been loading it with RL7 for many years but found through testing that I would get a huge difference in drop at 200 yards if the temp was bellow about 10 degrees, so I don't take it hunting if its really cold. My velocities for my pet RL7 load are about 2200 fps at 80 deg F, 2100 fps at 25 degrees F, and at -15 degrees after letting the ammo and rifle sit out overnight I got an average velocity of 1780 FPS! I tested several different powders over about a week when it was really cold and settled on RL10x with a Federal magnum primer. At 60 degrees I got 2165 fps, and at -20 F it was 2080 fps.
The magnum primers are something I discovered in the last couple years to make an enormous difference in the cold to combat that velocity drop. I am planning to retest most of my rifle with magnum primers. It also helps alot in pistol calibers as well. I also test my defensive pistol loads at -20 F as well.
And then to make it even more difficult, there are some powders that are inversely temp sensitive, so the pressure goes up at cold temps. The picture below was a 300 blackout loaded with Lil Gun with the max load listed in the hodgdon manual. This load shot completely normally in november at 40 or 50 degrees and showed no pressure signs. At -18 deg F. The primer pockets are expanded almost big enough to fit a large rifle primer.
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Factory Precision Hunter does give me pretty consistent sub moa groups in that gun though, so I think I'd still take his money. I don't usually shoot 5 shot groups though, I may have to test that.
Once you get a rifle, especially a budget rifle, that does consistently shoot moa groups or less, it's hard to accept anything less. If I pay $1000+ for a rifle these days, I expect at least 1 1/2 moa performance with premium factory ammo and I've got a few $500 guns that deliver this. All of my Savages , my Ruger American .308, and my T/C 6.5cm will do it.
But since you are.... What do you think causes the large groups? Ball powder, barrel shift...?
