I put this together for a friend after trying to think of a way to reuse some of my spent 7.62x54r shell casings.

Step 1: Materials

You will need the following:
2 - 7.62x54r shell casings (or similar)
Cyanoacrylate Glue (Krazy Glue)
Drill
3/16" Drill Bit
Wire Brush for Drill
A "Bic Round Stic"-style pen
A Bolt

Step 2: Drill Out Shell Casings

Use the drill bit to drill out the part of the shell that the hammer strikes. You can use the dent from the hammer strike to help centre the drill bit. (REMEMBER: Only do this to empty/used shells)

Step 3: Clean Up the Shells

Use the wire brush in the drill to clean up the finish on the shells. I recommend wearing gloves. Don't forget to brush the base of the shell.

Step 4: Glue Bases of Shells Together

Glue the bases of the shells together like so.

Step 5: Insert Bolt

Add glue to threads of bolt and insert in one end of your pen body as we will now call it. See picture.

Step 6: Insert Pen Parts

Take apart your pen. Remove the ink cartridge from the removable shroud thing (see picture). Add glue to the shroud thing and insert it into the end of the pen body opposite the bolt. It should be a tight fit. You may need to build up the shroud's thickness with tape. See picture.

Step 7: Finishing

Allow glue to dry (recommend 24h), then use the wire brush to clean up any residue.

Insert ink cartridge.

You are done.

Feel free to recommend improvements.