Gun Control & RKBA

It's essential a sheetmetal frame with a few reinforcing, structural beams inside. There are some other hard spots besides the beams: the hinge area, the lock area, the power window mechanism. And of course there's sound-deadening insulation, weatherstripping, and some wiring harnesses. If a bullet hits something solid it will either deflect (with deformation) or simply splatter. But if a bullet will penetrate 12-16 inches of meat (which is what tactical, expanding ammuntion is designed to do) then a combined eighth of an inch of soft steel won't stop it.

Understand it will rob the bullet of energy, and will make the bullet expand. Both of these will reduce penetration is whatever is past the door. I'd rather be hit by an already-expanded, reduced-speed bullet than the alternative, given a choice.

Cars today are "built like tanks" with respect to collisions with other large objects; there's a video of a 2009 Chevy Malibu in a collusion test with a '59 Chevy Bel Air that makes the tanklike aspect of the passenger compartment of the modern car abundantly clear.

But being able to stop a bullet, which focuses all of its energy very quickly on a very small area is different from having two big, broad cars collide.

This page might be useful... a guy experiments with the protection a mid-to-late 80's Buick door would give.

He puts some posterboard behind the car door to see what would happen with the bullets after they penetrated. The bullets do penetrate, but they are also seriously deflected, spinning and tumbling and slowing down.

https://www.theboxotruth.com/the-buick-o-truth-3-pistols-and-car-doors/