I agree with omegasmoke, the Federal 209A is my personal choice above the CCI 209M.
"Hottest" is a hard question to answer, there are a few other factors to be considered, and all 209's are not created equally.
You have "HEAT", "PRESSURE", and "TIME" that need to be factored in for best ignition. One primer may burn hotter, one with more pressure, and another may burn longer. It is the primers with the best combination of these factors that will work best.
If I am going Hunting, I will have Federal 209A's in my rifle. Our December muzzleloading season can get well below zero here in Michigan, I am not going to have a weak primer in my rifle that just happens to work in August when it is 90 degrees outside.
If it gets really cold in your area, try one of the lesser primers and you will see what I am talking about. I have at least 10 or 11 different primers that I shoot with, some breech plug designs (custom) would allow me to use the weakest and probably never have a problem, but I would never chance it with an animal on the line.
