[m21sniper]

Supposedly optimum penetration for a frontal shot is 8"-10", but many shots are not frontal shots. You might need to punch through the BG's arms, a car door, a drywall, window glass, etc, etc, etc before you get to the vitals, or it could be a big jolly fat man, or perhaps even some sort of wilderness critter- hence the rationale' behind having deeper penetration.

The FBI arbitrarily sets the mandatory minimum penetration depth threshold for police ammunition at 12" in 10% gelatin. Some consider 15" to be ideal, others think 18" is ideal. To me, i think right around 12" is the ideal penetration depth for private citizen self defense ammo. I can see why cops and especially soldiers would want significantly more though.

The test performed in the OP are the "Denim tests." These results are all very impressive.

The performance of the 10mm 135gr (supposedly it achieves 5.56mm type destructive fragmentation) 9x25 115gr and the .45 ACP 230gr are especially amazing.