That's why I said before I think it was a planned drill and after everyone plays dead he gets a different gun then goes back in and really starts shooting real bullets and killing some of them. They are expecting shots so they just play dead and don't move.
Go back to prior breads they have been posted
This is the second part of it after he makes the first round of shots and comes back to pick up the magazine that was laying in the floor before he entered the building.
https://media.8ch.net/file_store/3a6568e1fa770b27ac93ae664d930df8e1270d9fb482b0f9fdf4d63655aa2c31.webm