Mistermix at Balloon Juice studies it:
One of the talking points about the Tucson shooting is that the gun used is “just the same as the one police use”, and that’s true the Glock 9mm pistol is a common police sidearm. But, police carry it with a 15 shot clip, not the 30+ shot extended magazine pictured here. By the definition of the assault weapon ban, it’s an assault gun with that extended mag.
In Saturday’s shooting, it was only because of the heroic actions of Patricia Maisch, who grabbed the extended magazine from the shooter’s hand, and the lucky break that his next magazine’s spring was defective, that the shooter was limited to 31 shots.
Joyner differs. Remember that Loughner left an image of that extended mag on his MySpace page. He was a very adept gunman, and tried to kill as many innocents as possible.