When Western Powders first introduced TAC around 2000 or 2001 (I'd have to look it up in my loading notes) they claimed it was very temp-resistant (have heard they don't anymore). I'd been running cold tests with various powders for close to a decade by then, because I'd had some really wonky stuff happen when hunting here in Montana down around zero.
That winter I ran some more tests at just about zero, including TAC with a load with 50-grain Ballistic Tips I'd used during summer on prairie dogs. It averaged EXACTLY the same velocity as it had at 70 degrees, which is the one and only time that's happened in all the cold-weather testing I've done--which had to be pure chance, because even when two strings of any load are chronographed during the same range session, one always averages a little different.
Ran several cold-tests this past summer and winter, and partly to check my results from 2001 tried several of the same basic loads I'd tried back then, to see if there was much difference in the results. There wasn't, though the .223/50 load didn't average exactly the same at zero as at 70. This was with entirely different chronographs than used back then, but the results were consistent.
