“A loaded gun magazine” aka just a magazine, you don’t describe a magazine as loaded. They just wanted to use the word loaded to make it seem more dangerous so the jury sees him as violent

Gun magazines can be empty.

Yeah sure, lemme just carry around an empty magazine and a box of ammo, then load the magazine. I’m sure whatever i have the gun for will patiently wait for me to load one bullet at a time, then load the gun.