How to Use a Dummy Round to Measure Your Chamber

Measuring the chamber of a firearm is important for a number of reasons. For instance, if you reload your own metallic cartridges in the firearm (meaning you manufacture your own ammunition at home), it's important to know the chamber length of your firearm so you can ensure that the brass casings are trimmed to the correct size. Finding out the chamber length using a dummy round is relatively simple, and requires very little in the way of tools.

Things You'll Need

  • Steel rod
  • Dummy round in the correct cartridge
  • Permanent marker
  • Calipers
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Instructions

    • 1

      Point the gun in a safe direction and open the action to visually verify that it is unloaded.

    • 2

      Close the action and place the steel rod in the barrel. Let the rod down gently until it touches the bottom of the chamber.

    • 3

      Mark a line on the rod flush with the tip of the barrel. Remove the rod from the barrel.

    • 4

      Place the dummy round in the chamber.

    • 5

      Insert the rod into the barrel again and lower gently until it touches the top of the dummy round. Mark the rod, again flush with the tip of the barrel.

    • 6

      Measure the distance between the two marks on the steel rod to find the size of your chamber.