The s&w two piece barrel is not tensioned at both ends like the Dan Wesson revolvers. It is only tensioned at the muzzle by a nut that requires a proprietary tool to tighten it when it loosens. s&w will not sell the tool.
Yes, S&W's 2-piece system is a bit different than the DW.
The S&W barrel has threads on one end, and a T-shaped flange on the other. The shroud is first placed on the frame with indexing tabs. Once the shroud is in place, the barrel is screwed in, and the flange covers the muzzle end of the shroud and tensions the barrel and shroud. Rather than a tool that engages a nut, the barrel is tightened with a mandrel that engages the rifling. It
is true (or used to be) the tool isn't available outside S&W, which is why barrel replacement is a factory-only job.
Since the barrel is (relatively lightly) screwed into the frame and held at the muzzle by a shroud flange, my impression is that it's tensioned at
both ends - or perhaps it's more correct to say that there's less overall tension and that it's spread out over the length of the barrel.
The one piece K-frame barrels, with traditional broaching are known far and wide for their exceptional accuracy.
Guns with traditional barrels can, of course, be very accurate. One area that can be an Achilles heel, though, is where the barrel tenon meets the frame - it can be an area of stress, that, when shared by the forcing cone, can affect accuracy if everything's not perfect. All else being equal, the 2-piece design is thought to enhance accuracy by relieving this stress. DWs, for instance, have a reputation for excellent accuracy.