http://www.ar15.com/forums/t_6_5/387...n_arfcom_.html
Click on the above link and go down to the post by Z71rat. He is the only one (other than Dark Eagle) that makes mags like that. IIRC though he is only able to do them for 223 based rounds and 308 based rounds.
The one in the pic you posted above is of a 308 sized mag. FWIW.
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