posted by gut
I'll defer to the gun experts here, but I don't believe so. AR-15 is a very small caliber bullet - I'm pretty sure a bunch of shots, much less one, aren't "blowing up" the lock. There's probably at least 10 better ways to get through a locked & reinforced door more quickly and effectively.
A .223 or 5.56 round (2 AR common rounds) are not blowing a decent lock.
However, unless the school windows are made of something better than normal windows (I honestly don’t know if they typically are nowadays or not) nearly any gun will blow through a regular window, AR or not.
So either way, no matter what type of gun (unless some small .22 pea shooter hand gun) an active shooter is getting inside a school through any glass door.
Unless, again, the glass in school doors are made out of some better glass (similar to bullet proof) and I am not aware.