While I agree whole heartily that 50 yards is the ideal zero if your red dot sight is your primary optic, I do not think this is the answer for the OP.
My understanding from his post is that he is running an ACOG with a backup RDS, such as this:
http://i19.photobucket.com/albums/b2...01NSN-DOCW.jpg
In which case the height over bore of the optic dictates that all of the graphs presented in this thread are not applicable to his set-up.
I still stand by my original post that he should zero his RDS at 25 meters (or less) and even then he is going to have to become very familiar with the hold over and chin weld required to use an optic like this.
This is for the simple fact that his RDS is not his primary optic, it is an "Oh Shit - BOOM!" optic designed for engaging targets at extremely close CQB ranges.
That being said thanks to Derek and Molon for the graphs. They are very insightful and I have already used them to convert a few Army 25m zero die-hards here at my work.