IIRC, Kragicon and Trapdoor front sights were attached via a dovetail and staked/soldered in place. Yours looks like it was just soldered straight to the barrel. I don't think an arsenal would have done it that way, just not strong enough. Another way to tell a purpose made carbine from a cut down is to measure the barrel O.D. at the muzzle. Not many people(except the savviest of counterfeiters) would go to the trouble of turning the barrel back down to the correct contour, therefore the muzzle dia. will be larger that normal.