See this thread:

A great visual of a 12 bore chamber is shown so extrapolate for 16 bore in your own mind. http://www.doublegunshop.com/forums/ubbt...0738#Post240738

Think about it, the proof house says 9" from breech minimums should be .051". Minimum wall thickness at any point near muzzle should be like .021".

Your gun is .018" at 9" from breech. That's like shooting a gun at .011" or .008" minimum wall near muzzle. Just crazy thin. Wow is that thin. Measure that gun again because I can believe a smith would do that.

I'd have left the pits and shot light loads before taking away that much metal.