Per Oakland County Sheriff Bouchard,
32 used cartridge shells and 2- 15 round magazines recovered at the scene, and the perp was found with 18 rounds in his possession. 7 individual rounds were found in his pocket and 11 in a magazine.
This likely indicates that at least 3- 15 round magazines were used.
I count 50 rounds in total, which would match a box of 50...
No mention of ammo type used- ie: hard ball/FMJ vs hollow point.
It sounds like brave heroes might have physically overwhelmed the shooter, possibly costing one or more of the individuals their life.