Smith & Wesson has never used a transfer bar on any revolver; all modern S&W revolvers, except the concealed hammer ones*, use a positive hammer block that prevents firing the round under the hammer if the gun is dropped on the hammer or even if the gun hammer is beaten with a heavy hammer of the other kind.
(I noted that exception in another post and was immediately jumped by the S&W haters saying that that proved S&W's are unsafe, etc. But a hammer block has one purpose - to prevent the firing of a round if the hammer of the gun is struck or the gun dropped on the hammer. If the gun has no outward hammer, the hammer can't be struck, and the hammer block is not needed. That would be common sense to anyone who has any sense, but there are some....)
Jim