COLD here in PA also. Looked out this morning and not a cloud in the sky so I knew it would be freezing. Then looked at the thermometer...said -1 then with wind I know it's way lower than that!
I've loaded a few .243's when I had the Striker a couple years ago. Used Varget and 70gr NBT's. Larry in SD is a great source of .243 data when he also had his Striker.