First, I would NEVER load higher pressure loads in a double.
When I first started loading for my Chapuis I tried IMR 3031 because I had a lot on hand. The loads crossed. I went to RL 15 and IMR 4831. The loads did not cross.
59 grains of RL 15 and 270 Speers shoot very good in my rifle.
65 grains of IMR 4831 with 286 grain bullets shoots very good, to 300 yards in my rifle.
Before I did any re-regulating, I would try a different powder.
I think 286 grain bullets are the best all round choice for the 9,3. I would be happy using the Nosler partition or the Woodleigh Soft point.
Try a different powder, one a little slower.