It is made of a metal softer than brass so it will never damage the chamber. The lock is inserted in the chamber then locked in place with a special tool. It can not be removed without the tool so the rifle is rendered safe and can not be fired.
For an instructional video of it's use go to Youtube and search "Omega Chamber Lock Rifle" and choose the top video.
Although Aussie laws are very strict on locking up your rifle these are a great idea because if the kids find the safe keys or the rifle is stolen it is rendered inoperable. Also handy for in transit use on shooting trips.