Everybody is enforcing the right to bear arms, mainly the Russian-built AK-47 and the shorter AKM. By the basic rules of physics, what goes up must eventually also come down, and those hundreds of bullets should fall at terminal velocity within a couple of minutes. We understand hundred of people get hurt this way every year.
Getting back to the cars, it’s abundantly clear that big is beautiful for the Saudis. A couple of the guns are gold-plated. From what we understand, this display is actually prohibited by law now, but is viewed as a way to display warrior-like power.