Kraig Biocraft Laboratories Inc (KBLB)

[es1]

Other agencys use clay as well. But i think its safe to guess that you are speaking of ballistic gel.
That is used by most agencys to approximate body density for projectile penetration.

But the gel has a memory. It returns to its orignal shape which removes any indication of impact depth.

Clay has no memory so it is used on impact testing. The projectile can bounce off but the clay remains impacted to its furthest point.

This can then be measured to determin potential damage to the person wearing the item.

So again your opinion is flawed.
Clay has been and still is used for military ballistics testing for impact damage.

And yes that is real world experience speaking.
I have been through the ballistics testing process before with BAE systems.
We had to build 5 humvees with "bomb proof" undercarriages.
These were then blown up with 200 pound blocks of clay in the passenger compartment as "victims".

Clay is a standard. Even if you dont like it