Also, if you are a detail-oriented person, look down the bore at the target; when the target is dead-center at 100 yards down the bore, it should be dead-center in the scope. Rounds fired with both aligned as well as you can should put the first impact on paper, then simply adjust. This is called 'bore sighting."
There is really no reason to "zero" at 25, 50, and 100; bore sight at 100, set the scope accordingly, and fire away. If rounds aren't on paper, then move back to 50 and try again. At 100 yards, you should be on and you can walk rounds to bullseye.
In my opinion, "optical center" is somewhat irrelevant. If I can't bore-sight and print on papaer, something is wrong that a v-block ain't gonna help.
And, for your edification: when you have the scope off the gun (or ahve a known zero), click through the full range, up, down, left, and right; so you know how much adjustment you really have.
And once you mount and zero the gun, note actual zero in number of clicks from stop - both horizontal and vertical.
It isn't that tough,just document every movement on the turrets till you are printing dead bulls (and printing groups, not individual rounds.) Once you have a solid zero, throw away the old documentation and start anew. never click a single adjustment into your scope that isn't written somewhere (on the bench), and I recommend come-uops taped to the stock so you know in the field where to go(or a BDC, if they make one for that scope.)