The RCMP are suggesting the designer didn't do this bit, and that it's required:

Former Cartridge Magazine Control Regulations

(4) A cartridge magazine described in subsection (1) 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.

although that used to be about riveting.