Interesting as I have heard others talking about using #4 shot for self defense.
That's #4
buckshot, which is much larger than just "#4 shot". #4 buckshot, which is a popular compromise load for tight urban areas with thin wooden walls, and stopping power, is usually comprised of 27 .24 caliber pellets.
This is in comparison to #00 buckshot which is usually 9 pellets of .33 caliber, or #000 buckshot which is most commonly loaded as 6 pellets of .36 caliber.
#4 shot, a popular load to make up for non-toxic wetland steel's poor ballistic performance as compared to lead is .13 in caliber. And the average number of pellets is somewhere slightly north of 200.