How to Make a Hole Punch by Repurposing a .357 Sig Shell (Bullet Cartridge)

Step 2: Remove the Cap (totally OPTIONAL)

You can remove the cap (the part which the firing pin compresses, causing the powder to burn), if you would like to have a clearance hole; by pressing a pin or other suitably slim item down the pin hole, you can clean the tobacco plugs from the cutter.  Keep in mind that the later brazing step may ("will most likely") interfere with the clearance hole. :-)

Stand off the cartridge from a hard flat surface by using a washer or machine nut which has a hole LARGER in diameter than the cap.

Find a very slim tool; a punch, a jewelers screwdriver, allen wrench, etc...  Place it down the open end of the cartridge and into the little hole in the bottom.

Now, using a small hammer (or other suitable stand-in for one) tap the punch gently...the cap should pop right out.