We did a car shoot-up 4 times when I was at my duty station in Oklahoma. We had a late 90s F150, a early 2000s Camaro, an early 2000s Impala, and a late 2000s Civic. We got a bunch rejected windshields(cracked/damaged) from our local glass installer, and over-laid fresh windshields over the vehicle as they got too shot-out to be useful. We first setup targets outside the vehicle to allow officers to shoot from the vehicle(simulating shooting from a patrol vehicle). Then we setup targets inside the vehicle to simulate shooting at targets inside the vehicle. Lastly, we shot up the vehicle at various points to see what a particular load would do to sections. We set up sand bags filled with shredded recycled tires to catch bullets, and setup up old Kevlar vests as well. We used what duty ammo we had on hand which included Speer Gold Dot, Winchester Ranger Bonded, and Federal Tactical Bonded. We did some .223, .308, and 12 gauge as well.
When it came to shooting through windshields, we found that the deflection of the bullet was different between the calibers. There was very minimal deflection if you were shooting straight into the glass, simulating the FBI's 45 degree angle, but if your target was off-center then the angle and curvature of the windshield caused major deflection. Generally bullets fired into a vehicle windshield deflect down, and bullets fired out of a vehicle deflect up...….but when you move off-center they start deflecting left-right too. In most scenarios of shooting into a vehicle, it was less common to shoot head-on into the windshield than to be off-center. Also, when we shot into the Camaro windshield the deflection angle was more acute than 45 degrees and we saw much greater deflection. The .40S&W loads faired the best with the least deflection and best penetration into the shredded tire sand bags. The .45 loads did second best. The 9mm loads tended to perform the worst including a few projectiles that bounced off the shredded tire sand bags instead of penetrating them. We also noticed that the 9mm projectiles were more damaged than the heavier calibers. We figured it had to do with the long ogive of the 9mm hollow point. The petals of the HP are much longer and thinner than the .40 or .45.....so likely less durable due to less metal. We shot a few rounds of .357mag Gold Dots as well just for the hell of it, and it faired almost as well as the .40 against windshields. I think this was due to the short hollow point ogive on the .357 which appears to be more durable than the 9mm.
When shooting through the car doors it wasn't as clean of a result as the windshields since there was a lot of random hardware in the doors that may or may not allow the projectile to pass through. We placed the shredded tire sand bags on the opposite door to catch the projectiles if they pass through first door. The 9mm and .40S&W performed about the same when it came to punching through the materials in the door and penetrating into the shredded tire sand bags. However, the .40S&W bullet was usually in better condition. The 9mm suffered damage to its hollow point and sometimes shed petals from it. The 9mm usually had little to no expansion beyond its fired diameter. The .40S&W was usually almost entirely intact, and would often compress the ogive and expand the diameter of the body in a fairly uniform manner. The best way I can describe this, is if you were to set a .40S&W JHP bullet onto an anvil and hit the nose of it with a hammer, it will compress the bullet down so that it flares out the body creating an expanded diameter. Many of the .40 loads did this when fired through the car doors. From what I remember, the .45 loads made it through the first door about 2 out of 3 times and penetrated the bags about the same depth as the 9mm and .40. The .45 loads tended to flatten out a little like the .40 loads, but not as much. The .357mag Gold Dots penetrated through the shredded tire sand bags and usually imbedded in the opposite door. They expanded similarly to the .40S&W loads.
I still carry 9mm off-duty, and I probably always will. It is a nice handling cartridge in smaller guns, and many other platforms. At least in my current duty platform, the full sized P320, I find that I handle the larger calibers very well in that particular platform and I don't mind managing the trade-offs associated with them. In other platforms, I have not felt the same way.