7.62 would have done it, 5.56 almost did and it's because the impact angle was ideal (right in the middle of an inward angle), all the rest failed miserably because of the shitty impact angle As rule of thumb for anything percussion (fists included) ideal impact angle is 90° Even the .50 with the wrong angle did jack shit, it did as much as any other caliber So in the end that whole test was slightly retarded because of this