the only barrel shrouds I have seen are integral to the barrel, not pinned. It was to protect the ejector rod from being damaged.Back in the day when Colt and S&W were the only major players in the police revolver market, S&W hyped their Military & Police Model of 1905 (later Model 10) as superior to any Colt due to the extractor rod being protected from bending by the shroud. I've been using revolvers for well over 50 years and have never bent an extractor rod on a Colt or any other. I did buy a revolver with a crooked rod, it was a Ruger Service Six, at a sizable discount due to a crooked rod. I took it home, straightened the rod and sold it for a sizable profit. On heavy recoiling guns the shroud can add a little weight to help reduce recoil, other than that I'd just as soon not have a shroud.
Add: The shroud contains a detent that acts on the rod, may help hold the crane and cylinder in line on revolvers that turn CCW. Colts turn CW and the hand pushes the cylinder, holding the crane in place against the frame, aiding in proper alignment with the bore. So sez an old Colt sales brochure.