You are right the barrel isn't prohibited the firearm is
LESS THAN 18″/457mm BARREL LENGTH RULES:
CC s. 84(1) “prohibited firearm” (d): If the barrel has been SHORTENED to less than 18″/457mm, after leaving the factory, “by sawing, cutting or ANY other alteration or modification” that forces the firearm into the “prohibited firearm” class.
If he took a Remington 700 30 cal barrel and manufactured an AR barrel from that, he's essentially making a barrel blank from a Remington 700 barrel (as he is cutting off the chambered portion), and is then making an AR barrel from the barrel blank.
prohibited firearm means(a) a handgun that
(i) has a barrel equal to or less than 105 mm in length, or
(ii) is designed or adapted to discharge a 25 or 32 calibre cartridge,
but does not include any such handgun that is prescribed, where the handgun is for use in international sporting competitions governed by the rules of the International Shooting Union,
(b) a firearm that is adapted from a rifle or shotgun, whether by sawing, cutting or any other alteration, and that, as so adapted,(i) is less than 660 mm in length, or
(ii) is 660 mm or greater in length and has a barrel less than 457 mm in length,
(c) an automatic firearm, whether or not it has been altered to discharge only one projectile with one pressure of the trigger, or
(d) any firearm that is prescribed to be a prohibited firearm;
The specific wording is "a firearm that is adapted from a rifle or shotgun, whether by sawing, cutting or any other alteration..." which means if it was once a rifle or shotgun, it cannot be made back into a blank, or un-made from being a firearm barrel.
A rifle barrel can be cut to any length (above105mm) and used on a firearm under 660mm, but not above 660mm.
A 10/22 barrel can be cut down to 5 inches and used on a Ruger Charger, but not on a 20/22 carbine.
A M4 barrel can be cut down to 5 inches and used on a LAR15 pistol under 660 mm, but not over 660mm.
The barrel is not prohibited, but could make the firearm as a whole prohibited.
Of course that is just my interpretation of the actual CC wording YMMV.
Direct from the Criminal Code:
Do you want to make a twin ?



























