DRT = D
A lot of stories about people getting hit with birdshot full-on, from the side and in the back from hunting accidents who not only survived but walked out to get treatment.
I have a friend who took a load of #8 in a hunting accident (ND from a fellow hunter really). He was shot in the lower calf & foot. None of the shot exited out the other side, and it wasn't because it hit bone. None of the shot pnetrated that deeply. I think the deepest pellet went 2 inches, and that pellet is still in there.
Even without the anecdotal stories - it's easy enough to figure out by shooting it into ordnance gelatin.
These results are in gel that really isn't too firm, generally there was deeper penetration in these blocks than normal:
But even with these blocks, you can see that #8 stops at 4" and it hasn't even hit a rib cage. One pellet makes it a paltry 5"
I would say that the 12ga makes a potent HD weapon, with the caveat that it's loaded with the correct ammo. You can take this very potent home defense weapon and reduce it's effectiveness tremendously by loading it with birdshot.