You can fit two 20rd mags sideways with a little slop, not enough to be a problem. One mag will also fit in each of the LBV pouches. Since they are thicker they fit tighter, but in my opinion I can deal with less ammunition for the handiness of the 20 rd magazines. I carry on my belt a Tactical Tailor pouch with two 30 rounders, and 20 rounders in the vest pouches. They work for anything I'll be doing.