CrossRoads:
I did not leave out hFE/beta, I was discussing driving the base hard so the device goes deep into saturation.
You want the current to be limited by the load resister and not the gain of the device
It is not necessary to drive a 2N2222 that hard to get it to saturate with a load of, say, 20mA. It saturates with 150mA of collector current with just 15mA of base current. Again, why use a transistor driver at all if you are going to use that much current from the Arduino?