All the newer S&W shrouded barrels work that way.
This is basically S&W's take on the Dan Wesson barrel, only the owner can't switch them.
The shroud and frame are "keyed" together on the front to prevent the shroud from rotating.
The barrel is threaded on the rear and has a flange on the front.
The shroud is slide onto the frame, then the barrel is screwed in until the flange torques against the step inside it shroud.
As above, the tool used to torque the barrel tight is a "spud" that has a sort of reverse "rifling" on it. This spud grips the rifling and allows torquing the barrel against the inside of the shroud.
I'd be surprised if someone doesn't start making replacement barrels and shrouds with a nut like the Dan Wesson so people can change barrels.