I've a 22" barrel on my 6Br.I run 87gr Vmax with 31grs N135,COL:2.331 was 35ths off the lands at the time of load development & running at 3070FPS.
I did try N140 but N135 gave better accuracy with the shorter barrel.
I would think starting around 29grs to 31grs N140 might give you something to work with.
My rifle grouped with the bullet on the lands & 35ths off the lands.My gunsmith advised me to load with a jump to the lands so your not chasing them as the lands erode.HTH ,Andy.