The r is your buffer, sounds normal. Perhaps another problem is holding you up, like camera cannot achieve focus.
To use the bbf technique to its full potential, you should be in af-c mode and menu a1 set to 'release' priority. If you don't have release priority set, the camera may focus with the back button, but if you recompose either on purpose or just slight movement, the camera may not fire since the focus point no longer sees focus. Release priority will allow you to recompose when you release the back button. This applies to the d7000, however the d7100 and d7200 will use release priority with the back button regardless of menu a1 setting.I've been having an issue with mine as well, I use back button focus and it beeps letting me know it is in focus and then I go to hit the shutter release and nothing happens. I'm in manual mode as well.
The r is your buffer, sounds normal. Perhaps another problem is holding you up, like camera cannot achieve focus.
Then number following the 'r' is how many shots you can still take with the remaining buffer capacity. "r09" means you can take 9 more frames before it fills.
Something else is holding the shutter button up.