Another low-traffic day on TFL, so here's an idea I toyed with a few years ago, along the lines of the "Depleted Uranium Needle At Near Light Speed" thread. Indulge me, here.
When I first got my shotgun, I tried to think of how to design a buckshot load that would open up super fast, stricly for indoor defensive use, with no friendlies around to worry about.
Picture a plastic shotcup, such as for birdshot. The "petals" splay outward when the cup leaves the muzzle, and air resistance catches them, allowing the denser pellets to travel down range unhindered.
Now turn the shotcup backwards, and make it out of extra stiff plastic. And instead of four flat petals, make it nine of them, each with a little cup at the end. Or four of them, with two cups along the length of each one. The opening of each cup faces outward, against the inner wall of the barrel. In each cup is a pellet of buckshot. (I realize there are practical considerations of what will fit inside a 12 gauge barrel, but this is a hypothetical topic.)
As the inverted cup leaves the muzzle, the gas pressure pushes each petal outward, and flings the pellets, catapult-style, all over the damn place.
The "practical" application of this technology is best summed up by Samuel Jackson in the movie "Jackie Brown":
"When you absolutely, positively got to kill every m****r-f****r in the room..."