A lot of Canadian firearms law is arbitrary, no doubt, but this is both arbitrary and really illogical. Regarding the fact that mag capacity is limited due to it being a shared mag, is this on the books? Or a grey area?
Not a grey area, although to some poorly trained and uniformed officers it probably is a grey area to them.
Look up RCMP special bulletin for businesses #72, and go on Questar's website for the LAR-15 Pistol Mag letter.
If you use magazines that happen to exceed the typical capacity of that firearm's magazine (5 for semi auto centrefire rifles, 10 for pistols, unlimited for rimfire rifles, and manually repeating rifles) it would be a really good idea to have some of this documentation on yourself if you need to educate enforcement personnel in the field.
Note I said "typical capacity" of that firearm's magazine. This refers to the capacity of the magazine that is
designed and manufactured for that firearm. Designed and manufactured are the key words here. It doesn't matter what firearm it goes into, it matters what it's designed, manufactured and sold for.
Ruger screwed up (understandable) with the BX-25 by saying it was also for the Charger pistol. Instantly makes it a shared rifle/pistol mag, and therefore pinned to the lowest common denominator (pistol, 10 rounds). May as well use a regular 10 round rotary one.
LAR-15 pistol magazines are designed and manufactured for an LAR-15 Pistol, and nothing else, therefore they are 10 rounds max. Slap it in an AR-15 rifle. No problem. Totally legal. Doesn't matter what it HAPPENS to fit and function in.
The problem here is Mossberg identified their rifle as taking AR-15 mags. This immediately means there pretty much is no magazine that's designed specifically for the MVP. So use AR-15 (Semi auto centrefire rifle, pinned to 5), or LAR-15 Pistol (pistol, max 10 rounds) magazines in it. The magazine that comes with it is probably an AR-15 rifle mag, so I'm assuming it's pinned, and should stay that way to be legal.
Remember, firearms don't have a magazine capacity, magazines do. A magazines capacity is limited based on which firearm they're designed, manufactured and marketed for. This is why Butler Creek 25 round 10/22 magazines are legal. Butler Creek never said they were designed for the Charger. They aren't, they're designed for (as per the packaging):
Ruger 10/22
Ruger 77/22
& AMT Lightning
All models the Butler Creek 10/22 25 round magazine is designed for are rimfire rifles, and therefore magazine capacity is unlimited. Because Butler Creek says so!
EDIT:
And as far as arbitrary and illogical... so what? What part of C-68 or any other firearm law in this country, and many others, is logical and actually addresses crime?