Worst case scenario, if it is only legal for a licenced manufacturer to create a short barrel, would there be anything preventing them from creating that short barrel out of a longer barrel (i.e., cut, crown and thread a 16"er)? Is there any distinction between manufacturing a barrel out of a steel bar as opposed to out of a longer barrel?
Also, the law says "a firearm that is adapted", not "a barrel that is adapted". Especially in the case of an AR-15, the barrel could be adapted before being affixed to the lower receiver, and you would not technically have adapted the firearm by cutting ... especially if the barrel had not been attached to that receiver before. You would merely have modified the barrel (legal), and attached that modified barreled upper to your lower (legal).
On the other hand ... that "or any other alteration" line could include swapping out a longer upper for a shorter one ... even if that shorter one came from the factory like that!
If you bought a lower receiver that had never had an upper attached to it, then affixed a chopped barrel, you would not have "altered or adapted" the firearm with a shorter barrel, no matter how your barrel was created.
Oooh, it's a mind-boggling maze, and you just know that's how
they want it.
I am inclined to agree with KevinB's assessment, because when you look at all these factors you realize that this law really can't apply to restricted firearms. The law is ridiculous all around, but pretty much unenforceable when it comes to restricteds. I'd be hesitant to put too many of these questions past the CFC or RCMP gun classifiers, 'cause if they rubbed both their brain cells together hard enough to come up with an answer, their heads would explode. Then they'd have to ban all restricted long guns!