A 40-260gr is gunna push the limit of a 1-28 twist. Ive shot the 40-240gr QT with 110-115gr BH209 and IMO it was on the edge of stability. It needed more speed or a faster twist.
Try some in the 230gr range unless you have a 1-20 or 1-22 twist. That is still a nice increase in SD/BC over a 200gr bullet. They are fairly soft lead