What's the largest barrel contour you'd use in the Marksman stock?
I've got a couple three barrels in Heavy Varmint/MTU/AMU contours, and they all fit in the Marksmans with room to spare.
The Marksman has the same forend as an A-5 in width and length. You could run a straight 1.250" and still have flats on the top of both sides of the forend, which measure about 1.450" out to out.
