That is another fallacy of ballistics jell and other test mediums.
It is not nearly the same thing as living tissue & bone, so "approximations" have to be made.
Skin isn't that hard to penetrate, it is just very elastic.
It may be that the bullet has to stretch it into the body cavity 4" before it makes a hole through it.
I don't know.
But if that is true, you could say
the bullet is already 4" deep inside the body cavity before it goes through the skin so it wouldn't affect penetration that much, and shouldn't be included in the calculation, especially twice.
So, 4" penetration in ballistic gel = getting through the skin? Personally, I don't buy it.
Reason being, I had a few #8 shotgun pellets dug out of my Bird-dogs hide one time after a friend tagged him by accident.
They sure as heck went through the skin, but they sure as heck weren't 4" deep either!
Another thing to keep in mind is that the normal adult males chest cavity contains about 1 1/2 gallons of
(are you ready for this) Air!
How many inches of ballistic gel is that equal too?
rcmodel