I wonder if any of you folks know if I test some handloads in this miserable cold mid-western winter what the side effects would be on the "groups" and trajectory. The current temperature is about 25 degrees. I have a limited window of time to get some loads worked up for Africa and need to pull this together in the next couple weeks.

Depending on the loads, you could be considerably off if you zeroed at 25F then hunted in the heat of African summer.
More specifics of your loads are needed.

If you must, you would be best sticking to the Hodgdon Extreme powders
H4895
Varget
H4350
Those I can vouch for having the least variability
from 40 F to 70 F, in my limited testing, first hand.

Check your zero when you get there.
Zero dead on at 100 yards at 25 F.
A scoped rifle with minimal drop of stock will then be shooting higher at higher temperatures.
Who knows, maybe only 2 inches high at 90 F?
You could live with that or make the adjustment.

If a double rifle, it will be crossed and low at higher temps with a sensitive load.

Really need to know more specifics to say ...

If it is below 32 F, forget about chronographing outdoors.
Or you could try some heater system to keep the chronograph above freezing.
What exactly is the point of your tests?
Load development?
Can you stick with factory ammo for a standard chambering, or do you have something exotic?
You may need to find an indoor 100-yard rifle range if the latter.
They have one on Long Island, NY, and in Dubai, UAE.

DRG says: "Kiss my liberal grits!"

quote:

They have one on Long Island, NY, and in Dubai, UAE.

There's a 300 meter one in Wiener Neustadt ...

If you can get a vehicle close to the firing line, leave the heater on high and keep the ammo in the warm. Needs to be warm all the way through. Warm the rifle back up between shots for final group and pressure testing. The barrel and cartridge temp matter, not the outside air temp. Just keeping the ammo inside your jacket and single loading would help if you shoot quickly enough to keep the barrel warm. Also a ladder test can help show what will happen as pressure (temp) increases.

I'm having a new barrel put on my 416 REM MAG.
I should be getting it back soon but I will not
reset my scope until it warms up.

The temperature and the altitude are 2 important factors ! For Africa it is better to load your cartridges 10% less or more, if you use it in your temperate country too, like the old english cartridges for Africa or India. In all cases you have to test your loads in the country where do you will hunt ! But dont forget that in Africa, especialy in the south part, the temperature are very different during the day, for exemple 5°C in the morning and 30°C in the afternoon ! On the another side, where is the problem if you shoot on a buffalo 1" too high or 1" too low ? If you shoot very quickly on a animal you need the factor chance for a good shot placement too !

Thanks Guys. I will be confirming loads I worked up this past summer. Unfortunately after I worked up loads in July, my son took over my shop for his woodworking. You can only imagine the chaos of having a woodworker amidst ones reloading gear. The sawdust even using vacuums, and air filters still negates any level of cleanliness. Anyway, I ask him to finally give it a rest and let his poor father finish his reloading. (These are good problems for a father to have) My testing this summer was for my Sako in .375 with RL-15 in 75 grains and pushing a Barnes TSX in .270 grains. My back-up rifle will be another old Sako chambered for .300 Weatherby using 4350 (70 grains)pushing a 180 Grain Barnes TSX.
I have agreed to let my son move back into the shop sometime soon to finish a beautiful hutch he has been building. Anyway, I will be going to Namibia for plains game in June so I wanted to get the loads completed and spend time in April and May practicing my shooting.Otherwise I would happy to wait until the weather warms up in April or May. I will take your advice and keep the ammo warm when I go to the range. I may take a Big Buddy Heater to take some of the chill off. As I write this note, it is snowing outside. Not too inviting for a relaxed period of target shooting?

Had the same problem a couple years ago. Loads where kept in vehicle and shot as fast as possible to avoid them cooling off. I was shooting a Brno 375H&H, RL-15 under 270 TSX's. Buddy was shooting a 416 Rigby, 350 barnse x's. Buddy was living in northern Canada and his temps where about -40C/-40f and where I live in southern Canada temps where about -24C/-10f. Neither of us had trouble with rifles and loads in Africa with temps 10 to 37C/ 45 to 100f. However, we had a lot of trouble with heat personally!