you haven't changed the magazine or the regulation. A detachable magazine for it that holds more than five rounds will be a prohibited device, illegal to possess whether you use it or not, even if you don't possess any gun that it fits.[/QUOTE]
That's why I specified that the magazine and the rifle would have to be changed so that the magazine would only fit this manually operated straight pull rifle (I better not call it a bolt action) and not fit any semi-auto. That would seem to comply with the letter of the law, unless there's some unwritten law that says "once a semi-auto magazine, always a semi-auto magazine". We seem to have a lot of unwritten laws in Canada.
I don't have an sks, so I'm not familiar with how the magazine mounts, but with many detachable magazines, it would be a simple matter to weld a lug to the outside of the magazine and mill a matching notch in the magazine well so the magazine could enter. The lug would prevent the magazine from being attached to a semi-auto. You would have manufactured a magazine for this manually operated rifle and it wouldn't fit any of those evil semi-autos.
Magazines of any capacity are legal as long as they don't fit a semi-auto. I know the SMLE magazine is specifically exempted, but wasn't someone recently advertising high capacity "trench" magazine for the "98 Mauser? Legally. In Canada.