Do single-player games with no mods work?

Do you have any special characters in your Steam username such as "." "?" or "<"?

Also, that person you linked just used the thinnest drywall sheets he could find, when about 40% homes have at least two layers back to back on EACH SIDE, and ZERO studs or beams between them, just pure plaster. That is not an accurate representation of an American home. It's a fun test but doesn't really say anything about overpenetration in buildings. 

Ok, but you have to be able to suspend your disbelief a little bit for that. There is effectively no tangible gameplay benefit to penetrating walls in this game, there is not one realistic scenario where you're going to want to penetrate through walls, any other time it's just a nuisance you have to navigate through.  I don't see bullets getting caught on walls and immediately think "oh it's really weird that this rifle round can hit 3 zombies", (which they already can)  I just think "well there's no reason to implement penetrating surfaces, so why would they?"   I'd be okay with bullets being refactored a bit, hell I'd even be okay with being able to create debris, bullet decals etc when you shoot, but this is another one of those situations where you're wanting to totally change how an entire system works because you want to simulate in gratuitous detail, and not because it actually has a positive effect on gameplay. This would just be a net negative on performance for barely any tangible upside.   Think about it, they'd have to factor penetration for every single type of material in the entire game, on top of changing to a primarily physics based implementation as you describe, which requires refactoring all of the skills and guns to match etc etc etc ad infinitum.    Zombies tank presumably because 1: We're not hitting the right part of the brain (hence why guns have a massive chance to crit as you level up, it's your character learning to consistently hit the right spots) or 2: because we're not even hitting the head which you DO have to manually target now. Zombies seem to feel no pain and only react to the physical force of the round hitting their body.    We can consistently 1 shot them with even the lowly 9mm and .38 special, we just have to have high skill levels and good moodles to pull it off. Damage stats on the guns pretty much ONLY matter when you're not critting, and even then there is not that much difference between a high powered rifle and a handgun in terms of shots-to-kill. The only thing that matters is hitting the off switch in the brain or severing the spine to make them crawl.

Wow!