But the canvas M-16 cleaning kit pouch fits a 40 rounder well with the bottom folded ove a little -I did that and added velcro to adjust to other mags. I use a couple...they are very servisable, but, single pouches.
I bought the "GRAD 2 Gunner" from Russian Combat Gear. It looks great but it was designed for the 45rd thinner/straighter 5.45 mags. I have not yet found a multi mag carrying rig or pouch for the 40rd 7.62x39mm mags but am looking myself.