The more I look at it, the worse it gets. This is Sub Bubba work. Why the apparent sleeve on the Butt Socket when a perfectly usable original thread could have been used? The shortening of the barrel. You would have removed the Flash Hider assembly, shortened the barrel and then reinstalled it. But no this has had its Flash Hider removed from the Bayonet Lug/Sight and then what looks like a dummy Flash Hider fixed by an internal thread into the barrel.