I blew jack and coke on my iPad.Although it doesn't affect ballistic resistance, modern NTSB safety standards require that semi windshields meet the 1-6P/LL standard. This mandates that they withstand an impact at 64 fps by a single lot lizard of sufficient girth and hideousness to require no less than 1 six pack be consumed before letting her slither into the sleeper.
The same study during the 80's attempted to set a limit on impact by spare change, but as they attempted to establish this value in a dollar amount, after 8 years of the last administration windshields would have had to be 2" thick and steel reinforced, so they dropped that requirement.
One thing that may be an advantage is most semi windshields are more straight up and down than the average passenger car. The downside to that is the height above the ground.
Last winter I saw a truck windshield that caught a rock from a snowplow. It left a quarter size hole and the rock was embedded in the passenger seat.
My guess is that the average pistol bullet is going to do at least as well as that rock. JMHO
I saw something to this effect posted by Mas Ayoob saying basically the same. Aim as straight as you're able due to angles and deflection and such. Windshield angles (usually) slanted so aiming from a bit higher (tough to do) and downward would help. As far as penetration, think about the Hornady FTX round with the rubber insert to help with penetration (keeps the cavity clear...). Works on 2-legged "barriers", too. :wink:The semis I have driven had the same thickness as four wheeler windshields just bigger. As far as penetration it will depend more on angle than caliber, if you hit it at a low angle there is a good chance of ricochet rather than penetration.