Finding Scope Center Height to Center Line of the Bore for Ballistic Programs
One of the questions the Sinclair technical staff receives on a regular basis is how one can find the scope center height to the center line of the bore for their rifle. This measurement is one of the variables used by most ballistic programs. The following is the method I use to determine this measurement, it is not exact, but its close enough for trajectory calculations for most rifles and ranges:
1.) Measure the bolt diameter and divide it in half. Example 0.700”/ 2 = 0.350”
2.) Measure the scope tube diameter and divide it in half. 1.000” / 2 = 0.500” (for 30mm tubes use 1.181”)
3.) Measure the distance from the top of the bolt in the rifle to the bottom of the scope on the rifle. Example 0.750”
4.) Add the numbers found in the formulas in steps 1-3 (0.350” + 0.500” + 0.750”= 1.600”)
Most load manuals and scope companies use 1.500” scope heights above the bore for their trajectory tables, since it is a very common measurement. Also most ballistic programs have 1.500” as the default measurement. If you are shooting longer distances such as 500 yards or further, the above formula should help you determine more accurate trajectories.
I personally try to keep the scope as close to the center of the bore as possible. Ideally, I like to have a 0.030” to 0.050” clearance between the bottom of the scope’s front bell to the barrel. I try different base and ring height combinations to achieve this clearance. For example on most of my Remington’s I use Ken Farrell bases with Leupold rings. I use their PRW rings for hunting and varmint rifles and their QRW rings for target rifles allowing me to remove my scope so I can also shoot with iron sights. If you have questions on how to determine the appropriate ring/base height, please call Sinclair International and ask one of our technicians for help.
Sinclair International Reloading Instructor/ Tech and Sales Rep