Case gauges are often talked about and recommended on the various reloading forums so I want to make sure that everybody, especially new reloaders understand something about them. The majority of well known gauges (Wilson, Lyman etc) are not made with a chamber reamer and they don't gauge cartridge diameter so just because your finished cartridge passes the gauge test doesn't mean it will chamber in your rifle. These gauges are used only to check case headspace against SAAMI minimum & maximum to help you adjust/set up your sizing die and to check case length for trimming purposes. On the other hand there are a few gauges such as JP Enterprises, Sheridan and a few others that I can't remember right now which are cut with a chamber reamer to minimum SAAMI dimensions. In addition to verifying headspace and checking case length they can be used as a final check for your finished rounds. If the round passes the gauge test, its guaranteed to chamber in your rifle. The converse is not necessarily true however. If a round fails the gauge, it may still chamber in your rifle depending on the size of your rifle's chamber. Before buying a case gauge, decide which one will best fit your needs. Also, the Sheridan gauge comes in a slotted version that lets you see the case/cartridge in the gauge and will help to diagnose chambering and die setup problems.