Indentation Formula: Calc w/o Vernier Caliper

[nata_eva]

Here is the problem, a bullet have been shoot from certain distance to the target board. when the bullet hit the board, it will make a small indent on it. Does anyone know what is the formula to calculate the indentation on the target board without have to measure the indentation using vernier caliper?

 

[f95toli]

There is no simple formula for such a complicated problem.
Although maybe one could up with an empirical formula if all the relevant parameters were known (material parameters, speed of the bullet, impact area etc) and only "simple" materials were used (material that deform in a reasonably predictable way over a large range of parameters).