I would say you should have at least one bullet (round for “Buffalo Head” ) at the end of a firefight. How many rounds you need would depend on location, number of purps, how good of a shot you are and several other factors. There is no way to give that a number. Also how many rounds and how often do you want to practice?
You don’t know how many rounds you need until it’s over, and that’s assuming you have some left.