Have you confirmed your twist rate, if you haven't I would do the tight patch method if nothing else.Hi Brent ... My Bergara barrel is 6 groove/ 1:8 twist. Also, I tried RL-26 / H1000 / N565 and got the "tumbling" with all of them. I know from other blogs I am not the only one experiencing this, but, I cannot isolate it to a cause.
By the way, the target distance was 100 yards, and the loads were not hot.