Apartment ceiling: how big of gap between drywall and studs?

[Stridulent]

Trying to mount the projector in my new apartment which is on the first floor. How big of a gap is there between the drywall and the ceiling? I'm super paranoid about hitting a water pipe or electrical circuit. I'm using a stud finder and I can even see places where there is a slight indentation, leading me to believe there is a stud there. But when I drill through the drywall, I get a gap and then hit something hard, but I run out of drill bit. The bit I am using is only 3 inches long, so I probably need a longer one.. But can anyone give me some pointers to help solidify my guess of where the actual stud is.