Basic Scope Question

[JASmith]

How close is close enough? If I were to get within 1/8" or so will that be sufficient to run ballistics calculations?

Thanks for the quick response.

Grunt

I lay a carpenter's tape across the scope and barrel and use the Mk1 Mod 0 eyeball to measure.

You can always do a sensitivity test with the ballistics calculator to confirm that the 1/8" or even 1/2" is good enough for your purposes. To do this, take a representative load and run with sigth height of 2.0". Then note the drop at the longest range you are interested in shooting at. Repeat with a scope height of 3.0".

The question to ask yourself: 'Is the difference between 2.0" or 3.0" enough to worry about for your purposes?' I yes, you're done. If not, try a closer range of scope heights.

You may get as much as a half-inch deviation above or below between the muzzle and the zero range. At much greater ranges you'll see larger distances. I did it for the Nosler 120 gr ballistic tip at 2520 ft/sec and a 100 yard zero. The drop at 1000 yards with a 2.0" scope height was -468.8" and with a 3.0" scope height it was -464.3" for a difference of 4.5 inches or ± 2.25 inches assuming 2.5" sight height was nominal and you were off by as much as a half inch in either direction.

That difference at 1000 yards is less than one-quarter moa in elevation. I would not be able to detect that with my shooting skills and equipment. I am usually very happy when I see 1 moa groups!. Others on this forum who can routinely turn in .25 moa groups might see the issue differently.

In any event, the advice mlmiller1 gives "You always have to verify ballistic calculations anyway so do the best you can do with your measurement, then check it in reality." is really top notch. It will correct even greater issues than an error of 1/8" in scope height.