The paper punch I have on my desk has a lever 4" from the fulcrum, and the punch pin is 0.45" from the fulcrum, giving a force amplification factor of about 8.9. If my hand pushes down with about 40 pounds of force to get the punch through a 3/16" stack of paper, then the shear force is 356 pounds, and the shear stress on the two 9/32" pins is:
356/(pi*9/32"*3/16"*2) = 3371 psi
That seems high... something to start with at least.
STF