Hoppe's elite is ok. Ezzox is also good. Call S&W customer service if your not sure what to use. I have a 327PC with a titanium cylinder and barrel shroud. I have used both of the products I suggested and they were fine. The big product to avoid is Hoppe's #9. Of course as you have already noted do not use anything lighter than 120 grain in .357. That will definetly ruin the cylinder finish.