High-density ball bearings?

There are matrials with higher density than uranium.

Michael Dahms

Your question cannot be answered with a simple yes or no. The velocity, weight, and thickness of the car door are critical as is the shape, density, and hardness of the ammunition. It would be fairly easy to calculate the kinetic energy of slug as long as you know the velocity of your high power slingslot. From that you can estimate your penetrating capability.

In regards to the ammunition, tungsten would be your best bet for a penetrator. While it may not be as dense as lead, the high hardness of tungsten will give you better penetration. Nanograined tungsten penetrators are being evaulated as a replacement for military uranium rounds. It may be tough to find tungsten bearings, but you could find scrap ingot you could cut up. You might even consider cemented tungsten carbide, readily available in bearings, density is only a bit less that tungsten at 15g/cc.

It is denser than lead. Platinum is denser than tungsten.

Michael Dahms

Yes, I got a little ahead of myself on this one. While the atomic weight of Pb (lead) is higher than that of W (tungsten), the tighter atomic packing of the W structure leads to significantly higher density. Both are cubic structures with a lattice parameter of

In comparison,the density of lead is 11.4g/cc, tungsten is 19.2g/cc, tungsten carbide 15.5g/cc, platinum is 21.5g/cc, gold is 19.3g/cc, and if you want to get really exotic iridium is 22.7g/cc, osmium is 22.6, rhenium is 21.0, whereas depleted uranium is 18.9g/cc. The maximum density of your projectiles essentially reaches as deep as your pockets go.