More Information related to this -- issued by the RCMP as clarification to 12 and 10 ga shotguns
https://www.rcmp-grc.gc.ca/en/firea...RJ7y_LjKhT0Jnti9b2aR-CMzmMdAKOLTIBHg6epgRoyal Canadian Mounted Police
Home Firearms What you need to know about the Government of Canada’s new prohibition on certain firearms and devices
What you need to know about the Government of Canada’s new prohibition on certain firearms and devices
Important notice: Update on 10 and 12 gauge shotgun classification under the new prohibition
On May 1st, 2020, the Government of Canada announced that it had made amendments to the Regulations Prescribing Certain Firearms and Other Weapons, Components and Parts of Weapons, Accessories, Cartridge Magazines, Ammunition and Projectiles as Prohibited, Restricted or Non-Restricted (SOR/98-462) [Classification Regulations] prescribing certain firearms as prohibited. One of the categories of the newly prohibited firearms include "Any firearm with a bore diameter of 20 mm or greater" (s. 95 of the Classification Regulations).
The Canadian Firearms Program (CFP) of the RCMP adheres to the Association of Firearm and Tool Mark Examiners' (AFTE) definition for bore diameter measurements. "The interior dimensions of the barrel forward of the chamber but before the choke." (Glossary of the Association of Firearm & Tool Mark Examiners by the AFTE Standardization Committee, 1st Ed. 1980). This is reflected in the RCMP's Firearms Reference Table (FRT) which clearly states that "...in shotguns, diameter of the barrel forward of the chamber but before the choke." The CFP also recognizes the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) standards regarding firearms and ammunition. The SAAMI chamber specifications for 10ga and 12ga shotguns do not include chokes therefore indicating that chokes are not part of the bore. Accordingly, it is the CFP's view that, in accordance with acceptable firearms industry standards for shotguns, the bore diameter measurement is considered to be at a point after the chamber, but before the choke.
Further, in making classification assessments of firearms which are reflected in the FRT, the CFP relies on recognized industry standard measurements. With respect to 10ga and 12ga shotguns, the CFP recognizes the SAAMI standard specifications which establish that the nominal (i.e. standard) bore diameter measurements for 10ga and 12ga shotguns are below the 20mm threshold (19.69mm for 10ga, 18.42mm for 12ga).
