30 yrs ago +/-
It may have been in the early 70's that a trend developed to use #4Buck in LE shotguns. I have an American Rifleman article by a guy named Jac WELLER that looks very late 1960ish (copy only) where he writes regards shotguns in southeast Asia in 1962 and analyzes the shotguns effectiveness on targets to 100 yds. WELLER liked #4B in his article, primarily 'cause more pellets increased the likelihood of more hits on paper out at 35-50 yds. He admitted that any buckshot past 50 yds was a roll of the dice, and at 100, near useless. (this from stock riot/trench guns barrels and IC and Cyl choke). WELLER did not address the smaller #4B pellets energy and penetration ( or lack of of it) at these intermediate distances.
My agency, as well as some other Fed outfits, used #4B as a duty load for a span of 10 yrs or so,m beginning about mid 70's then switched back to OObuck in the '90's. The #4B load was criticized for lack of penetrating power on heavy clothing, even moderate cover, and losing too much energy, too quickly, much past rock throwing distance. All this were negatives as a patrol round.
But, at bedroom/ hallway ranges, I see no reason why a load of #4B would not suffice.