For What it's worth,
I have #4 birdshot in my HD 870 (actually the rounds are in a 25 round sling in my safe-so i can grab gun/sling and go- I have slugs in there too, coz ya never know)
#4 bird is .13caliber pellets, and from house ranges you have the advantage of a really devastating load at close range. but what happens when you live in the suburbs/urban environment with buckshot? #4 bird is going to probably crack a neighbors window, and break skin at 125 yds, but buckshot will break skin at 350 yds and go right thru neighbors window and crack somebody's skull.
I feel that #4 bird is more of a socially responsible load WHERE I LIVE, that being said, what others do is fine, and I don't knock others choices because there are lots of variables in where we all live, how big our yards are, etc.
john l