What Happens to Bullets When They Hit Auto Glass?

Specifically, what happens to their trajectory? If it hits at an angle, does it deflect as a result, e.g., does a bullet fired at a windshield deflect upward? I'm not planning on shooting any cars, just wondering in case some knucklehead is running people over and I'm in the way.

Many videos on YouTube. Many go straight through

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Rounds that do well in the FBI gel testing protocols should penetrate the windshield glass while retaining most of their mass and still be able to reach the vitals of a person. There is an auto-glass stage to the testing protocol. My understanding is that bullets that penetrate the windshield from outside of the vehicle deflect downwards a little. One of my coworkers got into a shooting in which he fired through a windshield and, based on where he was aiming, the bullet did deflect downwards and impacted lower than the POA.

I’ve done a lot of training in and around vehicles. Quite often shooting through windshields is like a box of chocolates. But generally speaking with a lot of caveats, outside/in goes downward and inside/out goes upward. The exact amount of deflection changes depending on a variety of factors.

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Originally Posted by Lon

I’ve done a lot of training in and around vehicles. Quite often shooting through windshields is like a box of chocolates. But generally speaking with a lot of caveats, outside/in goes downward and inside/out goes upward. The exact amount of deflection changes depending on a variety of factors.

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This, precisely.. In general, bullets fired through a windshield (into the car) will usually deflect downward by several inches, because the bottom of your bullet nose is hitting the angled glass first, tilting it downward as it penetrates.

Story of one. Training with a regional FBI SWAT team.

Mid 80s Lumina. 62 g bonded HP thru a 10 or 11 inch AR at 50 yrds with an Aimpoint. IIRC braced on a backpack on a platform to simulate to top of a car.

I held just above the top of the T-Box on a "face target" and it dropped it in just below dead center. Maybe a 3 inch drop at 50.

Also confirmed that day that a 7 or 8 year old Body armor that had been in the back of a truck of a supervisor's car for the entirety of its life still exceeded it rating with multiple hits.

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Originally Posted by Lon

I’ve done a lot of training in and around vehicles. Quite often shooting through windshields is like a box of chocolates. But generally speaking with a lot of caveats, outside/in goes downward and inside/out goes upward. The exact amount of deflection changes depending on a variety of factors.

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This is the general rule... in the vertical plane.

https://i0.wp.com/www.tactical-life....50%2C150&ssl=1

From personal exprience, 1990 vintage Winchester 147 OTM will deflect off side window glass of a 1991 Chevy Caprice. Multiple times.
Will penetrate rear window.

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Originally Posted by TiroFijo

This is the general rule... in the vertical plane.

https://i0.wp.com/www.tactical-life....50%2C150&ssl=1

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That diagram is also correct for the horizontal plane as addressed in numerous papers by Alekseevskii and Tate and their contemporaries regarding the behavior of yawed impactors in targets (e.g., sloped armor).

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Originally Posted by the Schwartz

That diagram is also correct for the horizontal plane as addressed in numerous papers by Alekseevskii and Tate and their contemporaries regarding the behavior of yawed impactors in targets (e.g., sloped armor).

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I'll admit, it took me way too long to understand the WHY behind this.

But I finally realized it's basically a function of "braking". The part of the bullet that hits first is suddenly and rather abruptly slowed down. Causing the bullet to yaw in the direction of the braking. Now I see how larger caliber/higher mass bullets can help mitigate this problem a bit. And how bonded and monolithic rounds avoid the secondary problems of the jacket shearing off or beginning to flatten/mushroom.

I failed kinematics twice in college, but physics is pretty cool. Still prefer electricity, light, and magnetism though (I made an A in that course...).