Original Item: Yes, you ask, how can a simple stamped piece of metal be called a Mystery Tool? That’s easy. Not even the best of the references on the famous Mosin-Nagant series of rifles and carbines tell you how to use it correctly.

It has four functions: (1) a medium screwdriver; (2) a GO firing pin protrusion gage; (3) a NO-GO firing pin protrusion gage; and (4) a firing pin wrench to adjust the amount of firing pin protrusion. There is an additional rectangular cut that provides clearance for the lip around the bolt when using the firing pin gages. See the additional pictures to see how it is used.

The shallow firing pin gage is 0.075 inches deep, while the deep gage is 0.095 inches deep. The firing pin protrusion must be longer than the shallow gage but equal to or shorter than the deep gage. The wrench recess fits onto the firing pin to allow the adjustment to be made. The adjustment is made in one-half turns, and the index mark on the bolt head must line up with the index mark on the exposed end of the firing pin. The narrow slot on the end of the firing pin is intended as an index mark, although it is written in various places that it is a screwdriver slot. In most cases it is too narrow to accept a screwdriver blade.

The reason these functions have not been widely clarified, is that the Russian recruit, throughout the life of the Mosin-Nagant, was trained in classes by a noncommissioned officer; he was not given a book to read. Thus Russian/Soviet How To manuals that cover the uses of this tool are few, if any exist. We have not seen any.