The way I read it, you can't use the mag as an ammo carrier, it does not fully enclose the ammo.
I brought a 50 round factory box here with me to 'Vegas, along with 2 8 rd. mags (empty). The 1911 and empty mags were in a generic copy of the COM box you have (attached the TSA tag where the cable goes). I just kept the ammo box in my checked bag that the COM box was in. I flew Spirit (each airline has some leeway to add to the TSA rules, can specifiy different things- go to the TSA website for their rules first, then to the airline's for theirs).