I guess 66-8 is the new one I'm looking at, with the lock.

is the barrel 2 pieces? is the barrel covered by a "sleeve" or is it one hunk of steel""

Two-piece.
Denis

good, bad, doesn't matter?

why do they do this? Their website says nothing

Tons of information out on the S&W 2 piece barrels. A google search will give you a few hours worth of reading.

Bad: VERY few gunsmiths out side of the factory will replace the barrel if you want to swap it for a different length or if it gets bulged by a bore obstruction.

Good: Because the actual barrels are under tension like Dan Wesson's barrels a tiny number of target shooters believe S&W's "two piece barrels" create the most accurate revolvers S&W ever built.

Not so bad: Like nearly all S&W production revolvers made since about 1997 they have rifling created by eroding away metal with electricity. That means the lands and grooves do not have the square corners that broaches used to cut. Your favorite cast bullet reload for your old broach cut barrel might have to reformulated for a modern one or two piece barrel.

They do it to save money.
Cheaper to produce the two parts.
Cheaper to install & correctly index the front sight.

As noted above, few gunsmiths have the necessary tool to remove the barrel for any work on it.
Denis

Dan Wesson uses a two piece barrel system, a barrel and a shroud, and it works perfect, my Dan Wesson vented heavy 44 magnum is the most accurate revolver I own, my new 66 Combat Magnum has been a great gun, not as accurate as my DW44 , but for its size I'm very happy, and it carry's like it's not there at all all day long..

I have a new 2.75" 66-8 and a lot of older models with the traditional one piece barrels. I can't say it's more accurate than my others, but it is accurate. And I really like the look of the of it. I think of it as a big positive and one of the major reasons I bought the gun (the other reason being the new detent lock-up on the yoke rather than on the ejector rod which was famous for backing out and jamming guns).