Long story short.....I know the mil marks are only correct at the 4 setting.....but is the center dot the same at both the 1 and the 4 settings......thanks in advance.......

Should be, but as with any scope, always best to check POI vs. POA at the various magnification settings just to be sure.

I think OP is asking whether the dot changes actual or apparent size with zoom.  I don't know for sure, but the subtension probably changes with magnification just like the other marks in the reticle.  I can say that Firedot on the Leupold Mark AR 1.5-4x  and VX-R Patrol 1.25-4x are both .3 mil (about 1 MOA) at 4x and are in the second plane, meaning their subtension is only accurate at 4x.  At 4x they cover about one inch on a 100 yard target.  At 2x they cover about two inches of the same target.

If the question is about point of aim shift, no quality scope should do that and I would doubt that Vortex, Leupold or any other good company would ever intentially market a product that would shift POI with zoom.

Topic Moved

The center is still the center. The only way the POI should change is if you use a holdover or turn a turret. If you have a scope that changes the POI by changing magnification, something is wrong with the scope.

Let me see if this better presents my thought.......at 1X I am hitting POA.....at 4X I seem to be hitting lower. 50yards with 50 yards zero at 1X.....I might be losing my mind,,,,I'll try it one more time towards the end of the week....

Sight it in on 4x, then see what you get on 1x.

paralax

This^. Your aim and margin of error will be worse at 1x than at 4x.  Sight in at 4x.  Then, chances are good that your 1x group (while likely larger) should print on top of the 4x group.

Will give it a shot (ha, a pun!).......

Any holdovers whether mil dot, MOA or fancy BDC will not work on a variable optic with a second focal plane reticule. Only at it's highest power. If you want it to work at all, you'll have to pony up for a First Focal Plane reticule optic where the reticule size varies with what power you've got the optic on.

However, there is supposedly a mathematical formula for this:

Distance = size of target (in yards) / mils, multiplied by current magnification / scope's full power magnification.

Soooooo...

Say I measure a target at .9 mils in my scope and I know it's an 18" circle. I'm using a 1-4 optic and have my optic set at 3x.

Take our standard mil equation: 18/36 = .5 * 1000 = 500. 500 / .9 (size of target in mils) = 555.5 yards. Then, to correct for my optic being set on 3x instead of it's max of 4x;  555.5 * 3/4 = 416.6 yards away. So, the target is actually 416 yards away.  

That's what I've concluded in my own studies on using mils. If someone sees that I'm wrong, feel free to correct me.