Ran across this during lunch. Decent comparison of 00 buck, #4, and #7 at what I would consider a typical home defense distance. Boomstick looks to probably be using a cylinder bore 18.5" barrel. Neither scientific nor controlled, but enough to show relative terminal effects, at least in terms of impact and pattern.
https://youtu.be/uERIjpiBvog?t=278
Essential takeaway is that at close range, all pack a serious punch. Heavier shot will have more penetrating power, obviously, but the birdshot is nothing to sneer at.
Brad
That video actually punctuates what I was about to mention.
From a shotgun setup properly, at home defense ranges, buckshot makes such a tight pattern that it dispels all the stupid myths about using buckshot, shotguns, and birdshot for HD.
Part of what makes buck so effective is that it's 9 .38 cal pellets at 1200fps impacting an area smaller than the size of your fist under 10 yards.
Birdshot...how much does a number 8 pellet weigh? They're smaller than the bb's from a bb gun for crying out loud.
Would it suck? Sure. But it's designed for hunting birds not people. Right tool, right job.
Buy an actual HD shotgun, or a barrel for your shotgun for HD. They're cheap.
Practice.
Load it with the appropriate ammo.
Birdshot for HD as an idea should go the way of the tactical wheelbarrow, debarked chihuahuas, and serpa holsters.