The table is used administratively. It is not a legal document.
The firearms reference table is not the law. The law resides in the Criminal Code. The firearms reference table represents the RCMP's opinion on what the firearm should be named and what its classification is according to the current rules in the Criminal Code. It is used throughout the RCMP and other police forces across Canada. They use it to identify firearms, so if it is seized by a police officer, then the firearm can be properly identified and recorded in the police data system.
It assists the courts. If the firearm description is standardized, then the description remains the same as the firearm goes through the court system. You don't wind up with continuity problems or other legal issues in court. It's used by administrators in the firearms program to ensure the firearm is properly described and that they are applying the appropriate administrative rules to the firearm.
The classification portion is used likewise by police and officials to ensure that, in the case of policing, it assists with the laying of the appropriate charge, and with the determination of whether an offence has actually occurred or not. On the administrative side, the classification is necessary in order to apply the Firearms Act controls, to ensure that the possessor has the correct firearms licence, with the correct conditions. Some firearms need to be registered. This is a way of identifying which firearms need to be registered as well.