We have used it in schools in some pretty cold conditions say 20 to 30 degrees but not in that cold of an environment. I am now speaking only from logic and information I have read. In the conditions you are talking about I believe I would have a special mix to deal with that extreme cold. I would try the Mobil #1 Synthetic 0-W-40 for that application. Check the Mobile #1 Website to review the information. (Mobile #1 Synthetic 15W50 cold weather testing). It does not get cold enough where I live for some testing or I would do that. What type of rifle are you using. If it is bolt gun I would think the 0W40 would be just fine for the extreme cold.