I worked out that I could use camera.arc with the crosshair scaled very small so that when you look through the sniper scope you see the crosshair. Being very small it is not visible when not looking through sniper scope. Had the muck around with the placement of the sniper rifle to ensure the bullet hit pretty close to the center of the crosshair. It is a bit rough, but it works.
let me know if you want to see the script.