A 12 guage with #00 buckshot is a good defensive weapon. About eight or nine .32-inch pellets per shell with #00 buckshot. The #00 buckshot pellets weigh 60 grains, and are doing 1,325 fps.
With 6 shots you are sending out about 50 pieces of lead.
A 9 mm bullet is about 110 grains and travels around 1500 ft/s.
So each #00 buckshot has the weight of 4 or 5 9 mm bullets.
Ouch!
4 buck is the real killer.