Jerry, just to begin the answers (and I don't know much about this topic) I know they've begun to do this within the last few years on certain revolver models where weight is a factor but it also saves manufacturing costs as well. The idea is to have a light weight metal shroud around a rifled steel inner lining or core.....again, to save weight. I believe this particular line of revolvers have scandium alloy frames and barrel shrouds and stainless steel cylinders and, I think, stainless steel barrels within the shroud. I believe the "Night Guard" series are made like that.

You can check the S&W website and look at the "Night Guard" series and see, but I don't think the technicals will mention anything about the two-piece barrels.

Hoping other more knowledgeable folks will chime in here.