Pierce Load Calculation on a solid billet

I am doing a calculation on piercing a billet during seamless pipe extrusion. I searched online for a formula but onyl be able to obtain formula for piercing sheet metal..which is

Piercing force F = P (perimeter) x T (sheet thickness) x PSI (shear rating of material)

It doesnt applied to a billet caused billet thickness is about 40 inches. It gives me a humongous force.

Some basic information of what I am trying to do is...

There is a 500 ton piercer use for making seamless tube. We want to know if 500 tones will pierce the solid biller or do we need to start by drilling a hole through billet,

Please refer me to a formula and dimension that I will need.

Thanks