Twist on the barrel?
Any marks on the piston head?
How low did you go on the gas?
Any issues with that ammo in other platforms?
I had a 9" barrel that would shoot 55gr reloads with some terrible groups (same ammo is great in my other rifles). Same barrel shot Serbian ss109 much much better. I've never had a problem with an OP rod. 2 pistons on the same day makes me think there's an issue with the rifle.