I have 5 current production(last 24 months) model 27/327/627s that are all just fine. In fact they are some of the best shooting S&Ws that I own.
Personally, I would never have completed the paperwork at the dealer's location. You should have refused the revolver on the spot and let him handle that.
Since we are past that point, simply call S&W. They will issue you a shipping label via E-mail and return the firearm to them.
DO NOT let the dealer return it for you if you have taken possession of the revolver. The downside here is that S&W will ship the firearm back to whomever shipped it to them. So if you send it, it will be returned to you. If a dealer sends it it will be returned to the dealer and logged into his bound book. That means you fill out another 4473 to get it back, pay another background check and wait another waiting period.