We used 76gr/R22/180XBTs in two 300 Winmags in South Africa and then drove over to Namibia. We had worked up those loads around 60deg at around 6000ft. South Africa was like early winter, frost on the ground at night and up to about 75 at noon. Namibia would get down to 20deg at night and 120 deg by noon! We never had any issues with bolt lift or change in zero, at least out to about 375yds. BTW 76/R22 seems to be one of those "accurate" loads in just about any 300 winmag. No doubt about it though, H4831 long or short will work just as well and it really is temp stable. I had no problems with R19 in 2 240Ws I had but in a 338WM and the 185XLC it was a problem. I had worked up the load around 60degs, but by December a storm came in and we were 10deg here in the valley! I checked my zero and I was all over the place and about 150fps slower! I went to H4350 and never had another problem. It's just good to test any load with any powder at extreme temps if you can. Good luck to you and you will love that 300 win!