Different manufacturers have/had different standards for choke and the constriction i.e the difference between the bore and choke and will also vary depending on the barrel ID, so the 'stepped gauges' are not for precision work. A Browning barrel will yield a different choke measurement with this type of gauge than say a Win M21 barrel.
I have the Galazan Pro Gauge which is actually a set of three fingers attached to a long rod with dial indicator. It also has a set of standards so you can measure the barrel ID. I wouldn't use anything else.
I do have a stepped gauge from Galazan but would only use on Supers which are close to what the Galazan stepped gauge shows, usually.-Dick
