Understanding total mil adjustment / center-line of scope

[littlepod]

I have two rifles, identical scopes - Athlon Ares ETR 4.5-30x56.

Tikka T3X 308 - 0moa rail - 1.80" height over bore. - 100 yard zero
Tikka T1X 22LR - 25moa rail - 1.96" height over bore. - 25 yard zero

With my 308, I have 14mils left of upwards adjustment.
With my 22, I have 18 mils left of upwards adjustment.

I would think most scope makers would try to make center-line of the scope relatively center to common zeroes. So I was expecting more of 16mils left on my 308, and given the short distance zero of my 22, I'd expect also 16 mils, + 25moa base, so like 23mils left. (25moa = 7mils?)

How/why does this math work out that way? Is this just a poor scope mfging to have the center-line be not as center? - Or scope mfg assume that everyone runs a 20moa rail, so they try to keep people's zero at the centerline for best optics clarity?

 

[Steel head]

Also depends on any tolerance stacking and barrel curvature.

14 mils isn’t bad for a 0 mount.

 

[Jack Master]

Scopes are typically made with the center of the available dial elevations at the center of the optic, looking straight out. The height over bore will start to immediately take away available dial height. Plus you'll need to add a little for the bullet drop in that zero distance. Your 308 with 1.8" of height plus .2" bullet drop (guessing here) will make the impact 2" below the center of the scope, this is 1/2 Mill immediately taken out.

Then there is a game of thousands of an inch. Lets look at just the scope base and the rings.
Your scope rings and base are about 6.5" apart/long. At this distance if the front mount is 0.0019" higher or lower than the rear you loose 1 MOA. To loose 3.4 moa (1 Mil) is .0065" of difference. If your scope base is off .0065 and your rings are off .0065 you just lost 2 Mils, this is before your look at the scope over bore and bullet drop added to it.

Just for kicks, switch your scope rings front to back and see if it changes. Might get a mil back, loose a mil or stay the same. Ya might find out its not the scope but other tolerances.

Now your Barrel - Is your barrel exactly true to your action? Could it be slightly pointed down due to being a long tube help up by one end? or could is be slightly pointed downward due to a manufacturing tolerance?

How about barrel harmonics, is your load tuned to have the bullet exit the barrel at the top or bottom of the harmonic frequency?

For the 22lr. at a zero of 25 yards and 1.96 height over bore your already drop 2.2 Mils to get to your zero, plus bullet drop.

These are all things that will come into play. I agree, it sucks losing that available adjustment right out of the gate, but its the nature of the beast.