My informal testing was done on windshields that were still in the vehicles. I actually "tested" this theory some years ago, and posted the pictures of the testing, when some so-called "expert" spouted off nonsense that a person needed at least a 40 caliber to penetrate a windshield of a vehicle. So I informally tested his scenario, with a 9mm, a 40S&W, a 45acp, and a 44 Mag, just for grins. Not one failed to penetrate the windshield, and would have easily, IMO, taken out the driver or passenger of the vehicle. (the vehicle was a four door 1975 full-sized Plymouth.) One FMJ 9mm even went as far as stopping inside one of the taillights after being shot through the windshield, and going through both the front, and rear seats! I tested at about 25 feet in front of the vehicle.I have seen those also even shot at some myself.
there is a difference between a broken windshield propped up while someone stands over it shooting down at an angle to make the impact 90 degrees to the glass
and a windshield properly mounted in a vehicle at an angle designed to have the best deflection it can for aerodynamics.
Now make that a moving vehicle that creates its own upward air turbulence and penetration becomes an issue.
Real world vs shooting range can have a big impact on outcomes and I think people should be aware of this before they have to find out the hard way (heaven forbid).