Scope calibration: Do I understand this correctly?

[rg1911]

I'm working to progress from Kentucky Windage estimations to real calculated scope adjustments. Having read numerous posts here, please let me know if I understand the goal and the procedure correctly.

Part 1
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The immediate goal is to see if your scope tracks correctly. That is, if it's an MOA scope, that X number of clicks moves the crosshairs the correct amount. For instance, with 1/4-MOA adjustments, 8 clicks should move the crosshairs 2 inches at 100 yards, or 4 inches at 200 yards.

To do this, you can make the rifle/scope combination rigid, or remove the scope and clamp it such that it won't move. Then, with a grid target at exactly 100 yards, see what happens when you adjust the elevation and windage. This can be done in your back yard.

The percentage difference between what you expected and what you observe will be applied to your scope setting when actually shooting. eg: It might take 5 clicks to move the crosshairs 4 inches at, say, 400 yards.

Question 1: Should you use graph paper that shows finer graduations than just every inch?

Question 2: Is there a particular scope setting at which you should do start? That is, should the windage and elevation adjustments be at their midpoints?

Question 3: Should this be done at the lowest power setting, the highest, in between, or several power settings?

Question 4: Is the distance measured from the front of the scope or from the adjustment turrets? Or does the 2 or 3 inches difference matter in real life?

Part 2
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Shoot to verify that the calculated number of clicks moves your group the calculated distance.

Question 5: Do you do this verification at 100 yards, or 200, or ...?

Thank you for sharing your knowledge.

Richard

 

[Chanonry]

Re: Scope calibration: Do I understand this correctly?

You could tape a steel rule to a wall, simplifies things a bit.

It doesn't have to be 100 yard with a bit of maths.

I start at my 100 yard zero. Why would I do anything else, this is how I have to use it so my calibration needs to relate to its use. In practice it should not make much difference.

I would perform this test at a max, medium and low power, others may disagree

In practical terms a few inches is neither here nor there.

Part 2 is complicated by the likely errors from bc, mv and in my case ability! That has less to do with scope calibration in my opinion and is more of a system calibration. So you would want to do this at verified distances out to your maximum range

 

[rg1911]

Re: Scope calibration: Do I understand this correctly?

Use a ruler. [slaps head] I should have thought of that.

Many thanks for the voices of experience.

Richard

 

[bm11]

Re: Scope calibration: Do I understand this correctly?

What we did at Gunsite is really the only truly accurate way to do this type of thing, which was to have a really tall white target boar with an aiming point at the bottom, and a measured, confirmed 100 yard target. Using either a laser bore sighter or a DBAL, keep the scope on the aiming point while someone down range marks the paper. Dial up 5 mils and repeat. Dial up another 5 and repeat. ETC until you max the scope out, then measure the distances between the dots and divide that by the distance it should be (1 mil is 3.6 inches at 100 yards and 20 mils is 72 inches so if your scope actually tracked 74 inches your turrets track 74/72 which means .102 mils per click.)

If you haven't figured it out yet, on most scopes the error percentage is generally small and a non issue until you are shooting extreme ranges, at least with most scopes. Shooting generally also produces too much error over 10 mils to give you an accurate correction as well, which is why I pointed out what we did.

Finally, eight 1/4 minute clicks doesn't move an accurately calibrated scope 2 inches at 100 yards. It moves it 2.094", as 1 moa = 1.047" at 100 yards.