If you are using a plug in gauge similar to the Galazan model you are not getting a true reading of what the points of constriction are relative to the actual bore diameter of the barrel. Those types of gauges are machined and marked relative to the supposed nominal bore diameter such as 12 ga. = .729. My Galazan gauge measures .690 for the full choke ring. Subtracting the constriction from the (supposed) bore would then yield .039 or full. Many early guns were bored different from nominal so what you see from a plug in gauge can be very misleading. You need a bore micrometer similar to a Skeets Bore Gauge to determine actual bore diameter then points of constriction and do the subtraction correctly.
The Invector Plus Browning guns are back bored so the chokes are relevant to their actual bore diameter which make them seem open using a plug in gauge. Hope this helps, Joe.
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