I have owned one for several years with 2 heads and agree with the comments of the others. It is useful for bore and choke measurement. If I were buying one again I would just buy 2 gauges, one for 12-16ga and one for 20-28 ga; I noticed that Brownells no longer sells the 2 head set which sold for almost the same as 2 gauges. The best gauge IMHO for chamber measurement is one of the sissors type dial gauges.

Jim

I learn something every day, and a lot of times it's that what I learned the day before was wrong