After reading the FBI firearm ballistics wounding paper, my views on defensive ammo have changed. Heavier and hitting harder along with DEEP penetration are the keys to stopping the bad guy. No sissy loads allowed. I would keep #4 buck for summertime at a minimum. I prefer 00buck alternated with a big ole slug, one after the other. Those who live in colder climates where a bad guy might be wearing heavy clothing should seriously consider nothing smaller than 00buck and no reduced recoil loads.
JMHO.
Handgun loads are all heavy. 147's for 9mm, 158's for 38/357, 230's for 45, and 180's and up for 10mm. All loaded HOT.
cept I do have Corbon 165 grainer in a 44mag because at 1600fps outta a 6" barrel and I don't think much of any legged creature can handle that kind of wallup.