Update: today's temp climbed back up to a sultry 33 degrees at the range. Same box of ammo started out 6 inches high (I had adjusted the rear sight yesterday to try and bring up the POI). Stance I am using is down on my right knee with my support arm's forearm resting on my left knee. I switched to my tripod shooting stick with small change, improved about 2 inches towards POA in all directions (got tighter). Ran out of Federal and switched to HSM. Still high, but only about 2 inches (100gr heavier bullets, so understandable). Switched to a box of Hornady 300gr FTX and got a bullseye after zeroing for that ammo. Had to re-zero because that ammo is over 600fps faster, and I know the zero for the other two would be way off. Conclusion: I believe several things are in play: 1) the Federal's are somewhat temperature sensitive below freezing; 2) the barrel is still settling down as today makes only 80 rounds through it; and 3) I am certain the cold had to effect me for at least 2 inches of the drop. Bottom line though, and something I learned from this, double check your zero if temps drop well below freezing.