It's funny how finicky rifles can be. Mine didn't like 100's
My M600 sings with 100 gr bullets behind a max load of IMR4831. It is particularly fond of the Speer BTSP and the obsolete Nosler Solid Base.
Is it possible that you may need to load your 100 gr bullets to maximum velocity in order for them to stabilize? I'd try that before I gave up on the 100 gr pills, the most useful weight bullet if Texas hogs are on the menu, IMO.