I got one of the brass ones from Galazan's and I guess it's ok for what it does. However I found out first hand it will not tell the whole story.
I have a 16 gauge Model 21, barrel stamped Imp. Cyl and MOd. The brass gauge told me I had a "loose" Cyl. and Imp. Cyl. I assumed it had been opened sometime before I owned it. I don't have much use for a cylinder bore, so I had thoughts of screw in choke tubes. Then my gunsmith checked it with a caliper and it's choked .004 and .008 with .667 bore. In this case the brass gage was useless.
