The #40 is A.R.M.S., Inc's standard rear sight and is equipped with both 250-300 meter and 500-600 meter apertures. The 500-600 meter aperture includes a built in horizon line that helps lead distant targets and lets the shooter square the rifle to counter windage offsets if the rifle is inadvertently tilted. When engaged, the sight springs up to allow immediate use of the larger close combat aperture.
