Maybe silly question, but

[Sport45]

What makes a revolver a "flat top"?

 

[T. O'Heir]

The top of the frame is machined flat. A Ruger Blackhawk vs a Vaquero is a good example.

 

[ZeSpectre]

Not a flattop (Ruger New Blackhawk)

Flattop (Ruger Flattop)

 

[Sport45]

Thanks!