Jethro wrote:
I added a circuit breaker to my box yesterday. In the process, I
found that the ground buss their-in was already totally occupied with
existing white and bare-copper wires. In fact one buss spot had two
white wires held in one spot (under one screw). So, I figured it
would be okay for me to do the same with my new white wire and
bare-copper wire. So now I have three buss screws that each hold two
wires.

I have done it with no problem