Another AR magazine question and COAL

[Scoots]

I've used Larry Willis' "split case tool" to determine the COAL of my chamber for 220gr and 200gr bullets.
http://www.larrywillis.com/OAL.html

This gave me a COAL of 2.310" for my chamber, but this length does not work for my AR mags, which are 20rd. C Product magazines and 6rd. Stoner magazines. I had to keep reducing my COAL until I reached the "magic length" of 2.010" before my rounds loaded and fed from the magazine correctly.

What magazines are you guys using that doesn't require such a significant reduction in COAL from chamber to magazine?

Thanks for your help.