I have read a couple of posts in the thread about MOA not being correct or Chairgun not working with MOA.
For SFP scopes, stadia spacing can be either MOA or milliradian, at ONLY ONE magnification setting. It does not matter if the MOA or milliradian reticle is "correct", as long as you know what that spacing is. I usually measure mine, but Chairgun can do it for you if you want to assume that the manufacturer labeled things correctly.
Chairgun defaults to 3.438 MOA per stadia, which is correct for milliradians, but you can configure it to show whatever spacing that you desire. Say that you have an SFP scope with an MOA reticle, that reads MOA at 18x. But you want to use it at 16x.
1) Go into Chairgun and enter 16.0 in the "Scope mag" box.
2) Go to the "Toolbox" pull-down menu and select "Generic Mil-Dot Calibration". In the "Full Mill-Dots" box, enter 1.0
3) In the "Magnification" box, enter 18.0 because that is the magnification where each marks read 1.0 MOA (according to the manufacturer, but best to verify).
4) In the "Range" box, enter 100, because that is the distances where I know the spacing of a true MOA.
5) In the "Vertical Difference" box, enter 1.047, because that is what an MOA should be at 100yds.
You just told Chairgun that you are using an SFP scope that has true MOA at 18x, but you want dope to be correct for 16x. The result is that Chairgun will now give you the correct dope for your scope when using it at 16x.
Note: I used to use Chairgun and it works well enough, if you use it correctly, but I now use a custom spreadsheet to generate my dope.