Fortunately, I have never fired a handgun inside a motor vehicle.

Plenty of others have covered the applicable standards for self-defense, so there is no need for me to add anything to that discussion.

I have done quite a lot of testing the results of firing handguns through windshields. I tried a wide variety of pistols and revolvers in many popular calibers using every type of ammunition I could lay my hands on. What I learned is that without exception every handgun bullet fired through windshield glass was deflected from its normal trajectory, frequently by a wide margin. Not at all unusual for a bullet fired at a target in the driver seat through the windshield to completely miss the intended target. Many popular handguns and ammunition types will not even penetrate through windshields at modest ranges. Of those that actually penetrate there is no way to accurately predict any subsequent points of impact, even within a foot or more.

Windshield glass is very tough stuff that resists impact and penetration quite well, and most auto windshields are installed at angles that increase deflection.

I suspect that similar results would result from shots fired from inside the automobile.