Quote Originally Posted by RangeBob View Post
This is what "Special Bulletin for Businesses No. 72" says today:

5. Magazines for semiautomatic handguns which contain more than ten (10) rounds of a different calibre

Magazines designed to contain centrefire cartridges and designed or manufactured for use in a semiautomatic handgun, are limited to 10 cartridges. The capacity is measured by the kind of cartridge the magazine was designed to contain. In some cases the magazine will be capable of containing more than 10 rounds of a different caliber; however that is not relevant in the determination of the maximum permitted capacity.

Example:
Heckler and Koch P7 pistol chambered for 9mm Luger caliber:
The magazine designed for the 40 S&W calibre variant of the pistol will hold 13 cartridges of 9mm Luger calibre and function in the 9mm Luger calibre P7 pistol. This is permissible as the maximum permitted capacity of the 40 S&W calibre magazine must be measured by the number of 40 S&W calibre cartridges it is capable of holding, which is 10 such cartridges in the case of the HK P7 pistol magazine.

-- http://www.rcmp-grc.gc.ca/cfp-pcaf/b...323-72-eng.htm
By the definition that the RCMP are using to prohibit the 50 Beowulf mags as "dual calibre", 40 S&W mags are also "dual calibre". They are "adapted from the original" 9mm "design and the ability of the magazine to perform as originally designed has not been compromised by the adaptation".