I always wondered why that #9 or such "buffer" wasn't done, since there's so much wasted room between buckshot. Now I know it was !
The mantra is the Treasury uses #4, which I suppose Mel Tappan ("Survival Guns" paperback...still sound advice) popularized. The Wound Ballistics guys say #1 works best indoors, gets the job actually done, and doesn't overpenetrate walls and such. They claim birdshot creates a horrible wound (from which most eventually succomb, I assume), but these professional Wound Ballistics specialists are primarily interested in what STOPS them NOW...which usually, more reliably, means death...the other variations giving enough time for one to be killed. They rip Marshall & Sanow a new one too. Woah.
Hey...do you and yours know about (like you wouldn't) the V.N. room-clearing trick of reloading a 12ga. shell with $1.60 in dimes ? Said to fly everythere, and do a serious job. This is, I suppose, what Thurston Howell III uses as a Trap load.
During the 4th of July I like to light up our backyard BBQ with some of the magnesium dragons breath loads fired into the night sky with my benelli........... Great light and noise show. I suspect that 9 rounds of that at close range are the poor mans flame thrower. They are expensive but real fun as a "eye opener".............:o)
Bottom line for me is KISS principal. More can be done with a dove load at close inside the dwelling than most know. A 12 gauge ain't a Claymore mine albeit the old duckbill attachments make em such. I haven't seen duckbills for sale anywhere recently. A "friend" has a AOW NFA rig called a SERBU that has a duckbill installed . At 15 feet the pattern will cover an entire doorway if held sideways and fired. Downside is slugs are not included in the diet or self destruct "eaker" mode kicks in.
Stay Safe Muttly !