Nikon D6 Reference Manual page 877

d2: Max. Continuous Release
The maximum number of shots that can be taken in a single
burst in continuous release modes can be set to any value
between 1 and 200.
•
Note that regardless of the option selected, there is no limit to
the number of photos that can be taken in a single burst when
a shutter speed of 4 s or slower is selected in mode S or M.
D
The Memory Buffer
Custom Setting d2 [Max. continuous release] is used to select the
number of shots that can be taken in a single burst. The number of shots
that can be taken before the memory buffer fills and shooting slows varies
with image quality and other settings. When the buffer is full, the camera
will display r00 and the frame advance rate will drop.
G button U A Custom Settings menu
A Custom Settings: Fine-Tuning Camera Settings 825