During one of pre-alpha devblogs, Dean Hall seemingly programmed the top floor of the school/office to have a 100% chance to spawn a random weapon. During the devblog, he proceeded to use the weapon that spawned, it was an M4 at the time.
Here is the link to the devblog along with a time-stamp.
https://www.youtube.com/watch?v=346RQZZ75Jw#t=32m49s
Since then, the building would ALWAYS spawn a random weapon during every loot cycle. I would always find at least 1 gun if the school is unlooted, in the same place - the third floor. {F30603} {F30604} {F30605} {F30606} {F30607} {F30608}