2nd on the scope hight, would not have thought it made that much difference but at 780 out of a 300 Wby I was off by just over a .25 inch and it made 9 inches of adjustment trouble, any body have a best way to measure?
There are several ways to measure. It depends on what parts of the rifle you can access.
1. One method is to find a place where the diameter of the barrel and the diameter of the scope can be accessed in a single plane perpendicular to the line of sight with the scope zeroed. Measure three things.
Ds = diameter of the scope in that plane
Dr = diameter of the rifle action or barrel in that plane
Sp = space between the scope and the rifle in that plane.
H = the height of the scope over the bore
H = Sp + (Ds+Dr)/2
The above method only works if the barrel or action and scope are round and concentric with the line of sight and bore.
Other methods.
2. Find a place where the barrel and scope are approximately the same diameter then measure the distance from a point tangent to the scope and tangent to the barrel, perpindicular to the line of sight. Agian, the barrel and scope must be round and symetrical.
There are variants on the above methods which accomplish the same thing. These metods are not correct if the line of sight and the bore centerline aren't close to parallel. The rifle and scope must be round and conentric as in #1.
3. For high accuracy zero the scope on a target at the distance you'll use in your ballistic software. Mount a digital camera with a focusable lens on a claibrated linear slide set a few feet in front of the muzzle with the slide (or the rifle) adjusted to move in a line perpendicular to the line of sight and will move toward the centerline of the barrel. Move the camera so it'centered and focused on the zeroed reticle looking into the scope. Then by moving the camera only in the direction perpendicular to the line of sight, measure the distance the camera must be moved to be centered on the crown to the same same pixel on the CCD camera image as the reticle was zeroed. The direct measurement of how far the camera was moved is the scope height over the bore.
I have this equpment set up in my shop. It's very fast once the equipment is set up and will measure the rifle's scope height with no guessing to better than .001" I just lay the rifle on its side on a roll around table in front of my mill while using the mill vise to hold the camera and make the readings using the mill's DRO to .0001". Other linear slides will work like the carriage of a lathe or the spindle of a drill preess. This method will give the correct measurement even for very long zero ranges and with wedged scope bases where the bore centerline and line of sight not parallel and the line of sight is not centered on the scope's body.
I use a laptop with a USB camera. THey're not expensive but it helps to have one with a long enough focal length lens to get a clear image of the reticle and crown and it must be able to focus on the reticle and the crown. The cameras built in to laptops don't work well.
