Tac powder odd behavior

[wvbuckbuster]

Last year I worked up a load in my Sako Forrester 308 Win using Tac powder, Nosler 125gr AB, Win case and CCI 200 primers. Results were as follows:
Average for four shots
MV= 2957.2 ES= 20.8 SD= 7.7
Couple days ago, I shot this same load with the same components with these results"
MV= 3029.2
ES= 85.4
SD= 32.7
Was using my Garmin to check with. Group size went from .5825 to about 1 in. Temperature was within 10 degrees or so of each shooting session. I know the lower the ES, SD the tighter the groups normally but I have seen good groups with high ES, SD before. What has me puzzled is why they are higher now than last year using the same components? The load groups well enough that I plan on using it to try out on a whitetail. Just wondering if any of you have seen Tac powder act like this. I have used it in 223 and 35 Whelen without any major changes in readings. Your thoughts?

 

[salmonchaser]

I have seen that kind of behavior out of my 338 Jarrett; My 338 WM; my 06 and my 300 HH. In my case with the aforementioned I was tickling the tail of the dragon pressure wise, so to speak. I wan’t using Tac, probably RL 26 but I don’t specifically recall. No idea where you would have been pressure wise with Tac however. Actually with the 338 Jarrett and the 300 HH I saw erratic behavior by seating bullets into the lands also.
If it’s the same lot of powder and only 10 degrees warmer it sure seems like something happened to boost pressure.