No need for all this Editing unless you NEED a bullet in the Chamber for every render. Do this instead.
Create a new Node position it at the center of the gun. Parent the NODE to the gun. Position the Bullet properly, now Parent the Bullet to the NODE. For later use Save as Scene or Scene Subset. No need to edit a single thing.
The bullets load in place but by default cannot be parented to the chamber and spin with it like it does in poser. So the null wont do anyone any good. I suggest editing since it saves you from having to expose the hidden nodes everytime to aceess what you need which includes applying a different surface shader.
In the screen caps below you will see what you are looking for in the CR2 and what it should look like when you are using Notetab++ to change it. Choose “Replace All in All open Documents” regardless of how many files you have open.
Make sure you click on the icon that looks like several disks inorder to save multiple files at once.
Click thumbnail to see full-size image