I'm building a Manson type gauge from scratch and have thought about jjdawgs observations quite a bit. Really, the gauge could be built with any inside or outside point/pin/anvil/ball you wanted, depending on your goal.

See:

http://www.ebay.com/itm/iGaging-Dial-Tes...=item20d4ad8683

Sharp points would sure make for some difficult measurements, but you'd get closer to the bottom of pits/scraps/dings. Either inside or outside.

Flatter surfaces on either point would make for smooth movements and quicker measurements. But, are you bridging a problem area? What are you really measuring?

What exactly is barrel wall thickness? THE thinnest? Or random ball on a gauge that could span a narrow, but deep pit/ding?

I don't have the answer, but I've sure been thinking about it.

To me, an ideal gauge would be adaptable on both sides of the barrel. Maybe I'm over thinking it.