So, we have some interesting video of three separate 1/4 moa groups from the same lot of 100 rounds of hornaday 147 gr 6.5 ammo.
The setup was a new Tika 6.5 Creedmoor 24" @1140ish under really good conditions under a long proven nsx 1x15 with a match quality shooter. Video was shot with a 90x Panasonic camcorder and reviewed onsite with a display monitor. (Awesome setup btw)
The setup hardly matters, as I have seen this repeated several times. 140 eldm factory rounds shoot 1/4 moa consistently out to 3/4mile. Savage, Browning, Ruger, Jim bobs bubba works, doesn't seem to matter because H4350 and 140 eld in front of a gold medal match primer just works.
Same with the 143 eldx = 1/2 moa groups
In our video, we get clear 1/4 moa groups. Mostly much smaller...... the problem is they fall into three separate groups. (the same aim point) If we didn't have it on video, it would seam crazy.
Each group is small. The problem is not parallax or cheekweld. The total group size is approximately 2.5 moa aggregate if you were to look at all the impacts.
When I got home, I used a spreadsheet to look at Case weight. No surprise. I found three nodes across four grains of Case weight. This is more than normal in my experience for Hornaday brass, but clearly the powder needed to drive the 147 gr bullets was not as good as the H4350 in the 147 eldm Load. (I suspect superformance)
My guess, it's probably not your rifle. Try hornady 140 eldm. If it won't shoot with that load, you need to grow tomatoes instead.
Edited to add
I've burned more powder correcting cheek weld than any other issue combined....by far.