With my 460 Encore barrel I had achieved my best accuracy with reloads. The 240 gr. Hornady XTP Mag's and Nosler 260 gr. partition and 300 gr. hard cast bullets gave me the best accuracy.
In my Encore barrel the 200 gr. Hornady factory rounds would never shoot well, but they did in my S&W 460 Mag. If you are getting MOA at 100 yards with the Max loads, you may want to start reloading and find a good load with the bullet you want to use. It does not sound like a scope or mount problem, because you said the Max rounds did well.