How near would a 16th century musket's muzzle have to be for the shot to go through skull bone?

Question

An ancient Inca skull shows a hole made by a conquistador's musket shot.

http://macrocosm-magbook.blogspot.com/2007/06/hole-in-inca-skull-caused-by-musket.html

Answer 1

I would say the same fifty yards or less, probably less after seeing the Discovery "fastest guns in the West" series.
At fifty yards the old saying "hitting the side of a barn" fits the standard here, they had a hard time doing just that, hitting a square six feet square at fifty yards.
Then, the "ball" didn't penetrate the one inch ply board.

Answer 2

Depends on the purity and dryness of the powder, mass and shape of the ball, angle of the shot, windage, length of the barrel ... approx 50 yd or less.