I am doing the same R10x 26.1gr 39sbk's still need to chrono them just waiting on weather and time.
well remember that my barrel is only 18" i got 3320-80 fps with 39sbk and 25.1 grain of re10x with no signs of pressure so will just keep pushing .2 gr inc untill i see some signs
tony
anyone who has never made a mistake, has never tried anything new.