jack, indeed every measuring tool has a range and it is perhaps unfair to criticize a tool because of its range limitation. However, my Merkel 20-bore is .628 (as I recall) and that should not be outside the range of an instrument advertised as being able to measure 20-bore barrels.

In general the Skeets does deliver but it is a shoddy instrument, reflected in its price. Just reversing direction causes the indicator to move by a thou or so.

And then, of course, there's the head that comes off....