TTAG commentator int19h writes:
Some Canadian gun laws are so stupid that they serve as a perfect illustration that most anti-gun laws are written by clueless people and don’t actually do much. Consider their magazine restrictions, for example . . .
It’s 10 rounds for handguns, and 5 rounds for rifles – except that restriction is on magazines themselves, not guns they’re inserted in, and not on how you use the magazine (the crime is “possession of a magazine capable of holding N rounds”, not “loading a magazine with N rounds” or “inserting the magazine with N rounds into gun X”).
So a Beretta CX4 carbine can be loaded with a Beretta PX4 pistol magazine with 10 rounds, and it’s not a problem. All that matters is what gun the magazine was designed for, which is a ridiculous idea for obvious reasons. So one company sells an AR-15 “pistol” (i.e. sans stock), and they make 10-round AR magazines that are specifically stamped as being for that pistol. Naturally, they fit any rifle that accepts AR mags just as well, including “unrestricted” ones like Robinson XCR or Kel-Tec SU-16. And it’s all perfectly legal.
But wait, it gets even better. What about magazines that can fit different calibers, with varying number of rounds depending on the caliber? For example, some .40 S&W mags can hold and reliably feed 9mm cartridges, and obviously they will fit more of them, so a legal .40 S&W 10-rounder can fir 12 rounds of 9mm.
Again, because it’s the mags themselves that are restricted, not what you do with them, this is perfectly legal so long as magazine is “originally designed” for .40 S&W – which in practice usually just means is stamped with the appropriate marking.
All well and good, so what did the smart guys do? They import 5-round AR magazines for .50 Beowulf, stamped as such, so it’s all legit. And it just so happens that those mags will also feed 5.56 pretty reliably (because the only difference is in the feed lips, and it’s small enough that it doesn’t matter), and you can load around 15 rounds per magazine into it. And should someone make a “pistol” chambere d in .50 Beowulf, then 10-round mags “designed” for it would also be legal, and would conveniently accommodate 30 rounds of 5.56.