thanks for sharing that info! That's what I have been searching for.
Straight from the horse's mouth
Specifically you will want to look at section 4:
And section 5:
From section 4 we get that it is legal to use a magazine from a pistol in a rifle. Thanks to the fact that there are AR-15 and XCR based pistols available on the Canadian market that use STANAG magazines, it is legal to own 10 round magazines for those firearms. It is furthermore legal to use those magazines in any other firearm capable of using STANAG magazines.
It is important to note that THIS DOES NOT MEAN YOU CAN RE-PIN RIFLE MAGS TO 10 ROUNDS. The magazines must be specifically designed and marketed for use in a handgun such as the RRA LAR-15 or RobArms XCR Pistol.
From section 5 we get that the limit on a magazine is based on the caliber it is designed and marketed for and not for any other calibers that may incidentally be used in the magazine. This is interesting for us because there exist two cartridges, the .458 SOCOM and .50 Beowulf, which are designed to feed from STANAG pattern magazines, but are significantly larger than other commonly used cartridges. A standard 30 round 5.56 STANAG magazine will hold 10 rounds of either of these cartridges. This means that a magazine pinned to a capacity of 5 rounds of .458 SOCOM or .50 Beo will also feed approximately 15 to 17 rounds of 5.56 NATO. And yes, it is legal to do this, provided the magazine is designed and marketed for use with one of these cartridges.
These magazines are in rather short supply and are quite expensive. There are a number of other companies trying to bring more on to the market to increase availability with varying success. A site sponsor Northern Republic Magazine tried to import E-Lander .50 Beowulf magazines pinned to five rounds, but was blocked by the RCMP on a claim that the magazines were designed as dual purpose magazines and not strictly for .50 Beo. AFAIK the issue is still ongoing. There is additionally another company manufacturing 5/5 round polymer .50 Beo/.458 SOCOM magazines in Canada, but I am not allowed to mention them by name as several moderators are concerned about the legality of these magazines given that the RCMP has made no comment on them.



















































