Sounds weird but at the ranges that would be encountered in my apt it would hit an intruder like a one ounce solid yet loose a lot if not all of its penetration in the dry wall seperating our apts.
No, it will not.
Think about it. If it loses its penetration in 5/8" of drywall, it sure isn't going to penetrate flesh like a one ounce solid.
In the linked test above, #7.5 shot penetrated 5.9" (counting the deepest penetrating pellet). So assuming no bones, no intervening obstacles or limbs, and a perfect frontal shot, you've got enough depth for at least one pellet to get there.
I realize that "Don't miss" isn't the advice anyone wants to hear; but let's look at the facts:
The only way to stop a person is to shut down their brain by damaging the central nervous system directly (brain/spine) or by depriving it of oxygen to operate (circulatory system). Anything less than this leaves the choice to the attacker about whether they want to continue.
The central nervous system and vital organs are well-protected by bone, muscle and fat. Depending on the angle to the target, you may need as much as 12" of penetration to reach them on an
average human male (note that is
average).
Anything that penetrates 12" of bone and tissue is going to penetrate two 5/8" thick pieces of drywall and have a lot of energy left over if it misses the intended target.
Now I am not saying you shouldn't use #8 shot. I don't know you from Adam and that may be the best of a series of tough choices that suits your situation. I
am saying that you shouldn't delude yourself that #8 shot is going to magically act much differently in people than it does in drywall. An interior apartment wall isn't a very substantial barrier. Heck, you can probably put your fist through both sides if you don't hit a stud. If you are adamant that what you use for self-defense not penetrate that kind of barrier, then a firearm may not be the best choice for self-defense for that scenario.