When talking about Blackhawks, one must always distinguish between whether it's a standard Blackhawk (with the rear sight protection ribs) or a Flat Top Blackhawk, and the caliber to determine the frame size.
All currently made standard Blackhawk with the rear sight protection ribs are large frames.
All currently made Flat Top Blackhawk except 44 mag and 41 mag, are mid-size frames.