I have a Brownells 12Ga plug gauge and it usually comes up short in German shotgun chambers such as Sauers, Merkels and Simsons. These are guns made from the 1930s through the 1980s. That is even the case in guns marked 12/70. Most of these shotguns have .724 bores so everything is a little smaller than we're used to here. I have come to rely more on a good eye and an old steel 6" rule as was mentioned above.
But back to the original suggestion, that looks as if it would do just fine to distinguish a quarter inch difference in a shotgun chamber.
