Not knowing what finish was applied to the OP's grips, I recommend Formby's.
If the finish is a normal finish, I just soaked the grips in a small container of lacquer thinner.
This removes the Colt finish and won't harm the medallions at all, with some scrubbing of the checkering to speed things up.
This also won't raise the grain so little to no sanding is needed.
Usually a 30 minute soak was all that was needed, followed by allowing to air dry overnight before applying any stain or finish.