For playing with a calculator two penetration formulas are
the sectional density X velocity.
And kinetic energy/ area of cross section.
This are actually used for bullets on metal penetration which is not the same of course but still fun.

Don't get too carried away with those handgunner tests.
They are like the lever gun tests set up to also beat nitro express rifles half the time.

Apparently the paper wadding screws nicely with high speed rifle bullets by bunching up in front of the nose and sending the bullets of course.
When we have to hunt animals with 18 inches of paper on their foreheads we will be in trouble.

If there is a case for low velocity and hard cast lead, you would have to ask yourself why every pro african hunter changed to smokeless powders and nitro bullets 100 years ago.

Karl.