Cover all the bases and use a GAU-8 ;-) Takes a bit to wind up but
even those first rounds will count for something :-)

Amen brother! The API round will go in one end of an aircraft and out the
other without slowing down.

A lot of people are forgetting about range and bullet dispersion. The GAU-8
can reach out and touch someone at twice the range of most cannon, without
the huge loss in bullet density.

If you actually ever get into the dreaded knife-fight in a phone booth, the
other guy is going to have second thoughts about screwing with an A-10 when
the nose erupts in a huge cloud of smoke well beyond the range he can employ
his gun.