When I was there (late 70s, early 80s) the best masters were actually not official masters. The best were Whitehead masters, made by a student named John Whitehead. He hand filed a master with intentional deviations from ideal designed so that when you copied it, the copying errors would make it closer to ideal. Whitehead masters were copies of that hand filed key.
Several people from campus security used Whitehead masters instead of their official masters because the Whitehead ones worked better.
I had an accidental master for a while. My room key happened to function as a master when inserted halfway. I don't remember how I discovered that. I'm assuming that they have long since changed the lock systems, but on the off chance they have not, it was room 21 of Ricketts.