If indeed the white center is supposed to be an inch in diameter, regardless of what number the ring is, and some people are only getting about 3/4 of an inch, what is causing the difference?
If you are only getting centers of .75 - .77, how are you printing it? Do you just click the link and print from the page? I just tried it and the center white area came out about 3/4 of an inch.
I had downloaded the file earlier and when I print it directly off my computer, the white center comes out just slightly under one inch, somewhere between 15/16 and a full inch.
If your targets are coming out small and you have been printing from the web page, try downloading the file and see what happens.
Also, I printed mine out on 110lb cardstock instead of regular paper. It's available at most places that sell printer paper. I got a package of 150 sheets for about $4 at Wally Mart.