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.
Living in the area, my understanding is that one of he deceased, Tate Myre, was trying to stop him. Heroes come in all sizes & ages here.