I went back around and looked at the four U.S. majors. Southwest says loaded mags are fine but must have their own cutouts in the foam of the case. American says no loaded mags specifically. United and Delta plagiarize the federal code, saying ammo must be packaged in containers made for ammo, but don't say if mags have to be empty.
I guess its up to the traveler to decide whether they want to get into a battle of wits with the customer service reps at the airport.
No, thank on the battle of wits. Ugh!
American must have updated their site. It was more ambiguous when I flew.