@Odd Job and some others have it right on bullet deflection through windshields.
One of the best things I found online to illustrate what happens when shooting involves a vehicle is the Buick O' Truth:
https://www.theboxotruth.com/the-buick-o-truth-1-windshields-insideout/
https://www.theboxotruth.com/the-buick-o-truth-2-windshields-outsidein/
Bullets hitting glass at an angle do not behave the way you think they would, likely because glass is a brittle substance which crushes, unlike metals and other ductile and hardened materials. I haven't really found a site which explains WHY, but I have my own theory.
Bullets shot at a sheet of glass with the top angled away from you (like from outside to inside on a windshield) will deflect DOWN.
Bullets shot at a sheet of glass with the top angled towards you (like from inside to outside on a windshield) will deflect UP.
This is opposite of the way most people think would happen.
Why does this occur?
I suspect that it has to do with the point of impact on the bullet with the windshield and what happens as the glass is crushed and penetrated at an angle. (Meaning, not shot at perpendicular to the face of the glass.)
When shooting from outside to inside on a windshield, the angle at which the glass is thinnest is a downward angle. This represents the path of least resistance. So what happens, I suspect, is this:
The lower edge of the bullet's leading end impacts the glass first. This impact sends a shockwave through the glass at the instant of impact, which fractures and crushes the glass. The impact, being at the bottom edge of the bullet on the glass, produces a kind of "shaped shockwave" through the glass, which is angled downward. Thus the glass fractures and crushes at an angle through the glass that is along the path of least thickness: perpendicular to the surface of the glass.
The bullet WANTS to continue along on a straight path. This is basic physics. The fact that the bullet moves down in this scenario implies an outside force acting upon the bullet to produce that effect. When the bullet approaches the glass at an angle, the glass in the direct path of flight is thicker than it would be if the bullet were approaching at a 90 degree angle to the surface of the windshield. This represents a harder path to follow, especially since the shockwave of impact has fractured and crushed a much weaker path through the glass which is angled downward. So the bullet is deflected/pushed DOWN to follow a path of lower resistance.
When shooting from inside to outside, the opposite happens.
It would be really cool if I could find some close-up, slow motion video to see what actually happens and how closely my theory matches the evidence.
THAT SAID:
Shooting into ANYTHING, much less a vehicle, affects the flight ballistics and the terminal ballistics of the bullets. These effects may be generalized, but they cannot be predicted with accuracy individually.
Why? Because different structures made of different materials of varying thicknesses, densities, hardness, and other physical properties each produce their own specific effects on the bullets...and these vary depending on point of impact and the dynamic forces that are involved with each separate encounter from one material to another.
Shoot 5 bullets through a car door. One may simply pass through the outer and inner panels. The next might pass through the outer panel, impact on the glass window within the door (which produces a different effect on flight ballistics then for ductile metals), then the inner panel. The third might pass through the outer panel, hit the electric motor on the window regulator and never make it to the inner panel. The fourth might pass through the outer panel and pass through a void in the inner panel encountering only the cardboard/cloth cover on the inside of the door. The fifth might never make it through the outer panel at all.
And ALL of these bullets will suffer deformation of SOME kind as well as velocity changes...which will affect terminal ballistics if they DO hit the intended target within the vehicle. And they will be just as unpredictable, as well.