"Another big change I didn't notice immediately was the two-piece barrel. The inner barrel is a rifled tube, while the outer barrel (or shroud that encloses the rifled tube) is a single unit machined with an integral ejection-rod housing, topstrap and front sight base. The inner barrel extends through the shroud with the threaded end screwed into the frame. The shroud is keyed into the frame so it can't rotate and maintains a fixed orientation. There is a shoulder inside the shroud, and as the inner barrel is screwed into the frame, it tightens the shroud against the frame. Since only the inner, threaded barrel is rotated into the frame and the shroud is keyed into a fixed orientation, there is no "clocking" of the entire barrel assembly, which could rotate the front sight out of position. The end result is a more rigid, fixed structure. The topstrap has serrations that blend in nicely with the serrations on top of the frame and rear sight-mounting tang. Serrations reduce glare which can be very useful on a working gun, particularly one that may be utilized outdoors. The bottom edge of the ejection-rod housing has been cut to receive the steel ball mounted in the yoke that provides the new/old ball-detent lockup mechanism."
ht tps://www.shootingillustrated.com/articles/2017/9/27/review-smith-wesson-model-66-model-69-combat-magnums/
