Excerpt from Memorandum D19-13-2

Alteration or modification of a magazine

59. A prescribed cartridge magazine that has been altered or re-manufactured so that it is not capable of containing more than five or ten cartridges, as the case may be, of the type for which it was originally designed is not a prohibited device as prescribed by that provision if the modification to the magazine cannot be easily removed and the magazine cannot be easily further altered so that it is capable of containing more than five or ten cartridges, as the case may be.

60. For the purposes of the above, altering or re-manufacturing a cartridge magazine includes:

(a) the indentation of its casing by forging, casting, swaging or impressing;
(b) in the case of a cartridge magazine with a steel or aluminum casing, the insertion and attachment of a plug, sleeve, rod, pin, flange or similar device, made of steel or aluminum, as the case may be, or of a similar material, to the inner surface of its casing by welding, brazing or any other similar method; or
(c) in the case of a cartridge magazine with a casing made of a material other than steel or aluminum, the attachment of a plug, sleeve, rod, pin, flange or similar device, made of steel or of a material similar to that of the magazine casing, to the inner surface of its casing by welding, brazing or any other similar method or by applying a permanent adhesive substance, such as cement, epoxy or other glue.

61. This is not necessarily an all-exhaustive list and therefore not the only acceptable methods of converting magazines to five or fewer shots capacity for rifles/shotguns or ten or less for handguns.