I was going with what D-Zum said. IF it were a bullet, then it was one shot from far away and just hit the truck by random chance as it succumbed to gravity. (Which I assume happens plenty in that God forsaken city.) Dang odd place for a rock to have hit it with that kind of force and in that direction.
The pattern seems too engineered to be a rock. I wouldn't discount a stripped, broken bolt like, maybe, a piece of wheel stud.
I'd say definitely not a bullet, but could be a piece of metal like a lugnut. Have actually had 2 vehicles hit by bullets driving through Chicago. Hey Sean, ask Ev if she remembers coming back from the GNF in '86. Got hit on the Ryan around 35th street. That one had a long streak that started at head level at the leading edge of the sliding door, and ended with a perfectly round 'pocket' where it stopped. No penetration. Pretty sure it was from an overpass. The other was an actual puncture on the pillar, and it left the round inside the body of the car (we heard it bump down inside the body).
22 WMR will overrotate and destabilize with a 1:10 with most standard loadings. But maybe that's why it didn't penetrate. The plot thickens.
I had a customer get hit by lightning on the hi h highway on their passenger a pillar. Killed the car a it looked like a spot weld on the car. I'd say rock did it.
IIRC, I was driving and she was in the passenger seat, and it was head level. We didn't stop until we got back to Barnard's house, and then saw what it was.....then I had to listen to Buzz rag on me for 5 years that he let me drive his van and I brought it back damaged. Guess things haven't changed in Chicago much since 1984.
That it is not unrealistic to be a gun shot shows how nutty things are. https://heyjackass.com/ nice site keeping track of the fun.
Yeah, I think there's basically no chance it was a bullet. The abrupt line at the end of the scrape doesn't really line up with sample images I've found of sheet metal ricochets, nor does it make sense that it would slide to a stop on the sheet metal, then bounce off. I'm sure an actual bullet would have a more uniform exit scrape and/or actually tear the sheet metal. I saw the uniform grooves that dug into the van, and think I just let my imagination get the best of me. After having the idea that a bullet was that close to my wife's head, it was hard to be objective.