Here is a very simple, inexpensive, and easy to make tool for lapping the locking lugs on a bolt action rifle.  All you need is one old case, small piece of piano wire, epoxy, small spring, and some small washers.

The following procedure is what I used to made this lapping tool:
 

1. Resize and deprime an old cartridge case to fit the rifle.
2. Stick the case into some softwood or wax.  I used a small piece of balsa wood.
3. Remove the case from the balsa wood and make a small indention in the center of the circle impression made by the case mouth.  The small indention will hold the small piece of piano wire.
4. I use a 9-inch long piece of piano wire, which will fit through the primer flash hole and the hole in the bolt face for the firing pin.  (Something between 0.050 and 0.075)
5. I wrapped a small piece of scotch tape around the piano wire so it matched the flash hole diameter.
6. Sanded the end of the piano wire and inside of the case neck for good adhesion.
7. Mixed up some epoxy and pushed it into the case.
8. Placed the case with epoxy inside back on to the small piece of balsa wood and place the 9-inch piano wire through the flash hole and into the small indention in the balsa wood.
9. Placed in warm spot, let the epoxy flow into the case neck and harden.
10. Remove the balsa wood.

• Using pipe cutter cut the head off the case.
• Add some springs and washers for desired force. You are ready to start lapping away.  It does not require much force for lapping, let the lapping compound do the work.
• I used 600 grit followed by 1200 grit compound.