Magpul

[Angel Eyes]

Hmmm. Why couldn't an outfit like Magpul design a 10 rd mag that uses a 30 rd body?
They could sell tens of thousands of them to people behind the iron curtains, then have someone leak that if you take a drillpress/dremel tool/<insert common tool> and cut/remove this piece of plastic, a wolf spring will drop right in and make it a 30 rounder?
 

California has already been down that road.  Do a web search on "10/30 magazine"

[AJ Dual]

Apparently from reading the "look at the weird/cool stuff we can have in Canada, despite our overall crappier gun laws" threads and show-n-tell pictures on gun forums, that's what everyone with EBR's in Canada does, by that I mean the suppliers. Very simple blocks and rivets are all that are required.

If SHTF, everyone knows 1 second with a drill, 5 with a Dremel, or 20 with a file is all that's needed, and they have 20-30 rounds on tap.