At the range I am now going to, there are several dozen 18 wheeler tires stacked up on a hill for a backstop. While I was setting up targets, I noticed a bullet, what looked to be a .45ACP, stuck in the tire, and it wasnt even 1/2 way in. I guess it hit one of the steel support wires in the tires (the sides of the tires are the easiest to penetrate).
I was shooting it with a .22LR and 12 guage shotgun and all seemed to penetrate. However, I would think that most any bullet would be stopped if it hit in the right (or wrong) place.
BTW I no longer shoot at the tires becuase of the risks involved. Now I just shoot at a large dirt hill.