I didn't meant to imply that there were no possible situations where one might need to shoot through a barrier, only that as defensive shooting, I couldn't really think of any.
And I was also mostly influenced by the thought of someone using the car as a weapon, and needing to be shot, because of that. This is a different situation than someone IN the car shooting at you.
However, this does bring up the point, why wouldn't you aim at the person (who is the threat)? Now, I realize that aiming at the visible portion of a person firing from cover could easily result in your shot striking their cover instead of them, and shooting something that will penetrate that cover would be useful, if it happens to hit part of them, but is that the right basis to use as the priority when choosing ammo??
Also, again, I would point out the possible legal issues. We are all waaay to heavily influenced by the thousands of hours of "training videos" ("action movies and TV) we have seen since childhood, and while its natural to think in those terms, its not always legally justified to do what our action heroes do on the screen.
Consider, for a moment, as a private citizen, we don't have the responsibility to STOP the bad guy, we only have the right to defend ourselves from immediate threat. Here's a point to ponder, when the attacker is no longer an immediate threat, you aren't justified in shooting them. This is pretty established. For example, you might be in a High Noon shootout, facing down the attacker and trading shots (actually misses
), but when the bad guy turns away, walks or flees, even if he still has a gun, you're not justified shooting him in the back, if he isn't pointing that gun at you.
SO, consider that no matter what they did the second before, (or what they might do a few seconds from "now") when your attacker is behind cover (not pointing a gun at you that moment, not shooting at you, that moment, maybe you can't even see them) HOW are you, as a civilian, justified in shooting them, through cover? The TV hero is (its in the script), a COP can be, but are you and I going to be justified doing that??
The Jury will decide, I suppose...