I FEEL LIKE IM TAKING CRAZY PILLS! 0.8 Mil Vertical Zero Shift Session To Session

[HandgunHTR]

First off, how big are your 5-round groups?

Second, when you are shooting for zero, how many shots are you shooting?

If all you are shooting is 5-round groups, then there is a very good possibility that your zero check groups are actually falling within your cone of impact.

Before you start taking stuff apart, shoot a 20, or better yet a 30-round group to get your true cone of impact and your true zero.

If you did do a 20 or 30 round test to determine your system capability and true zero, and are using that to confirm that you are indeed getting a zero shift, don’t rule out focus and parallax as a potential cause. Most people I know have never taken the time to accurately set up their focus so that the parallax settings are true.

 

[Macintosh]

It’s strange that every time you adjust, when you go back to your other location you are off exactly the amount that you adjusted. If I understand correctly that was consistent multiple times. Makes me think it’s something about the location, not the setup…shot angle not accounted for + Ranges not exactly 100 yards?
0.8mil is a lot though. Hard to think of non-obvious changes that would account for a consistent shift that large.

Can you confirm 0.8mil= center of your 100 yard groups are off from previous zero by roughly 2.75”? How big are your group extreme spreads/how many shots are your zero groups?

To test if some “thing” is the culprit, you change only that thing and check function. So, to test it, you could zero at home, go to the other range and see if its .8 off again—but DONT adjust. Shoot and see if it is consistent though. Then go back home. If its still zeroed at home, Im betting it has to be something different between the ranges. .8mil is a ton for any one factor to cause, but with such a consistent error exactly matching your adjustments, I cant think what else it could be.