The Mountain Gun series from S&W was usually an N frame revolver with a 4” tapered barrel and rounded grip strap. Some variations were issued but that is the standard. On the N frame they were available in at least the following chamberings; 357, 41 Magnum, 10 mm(?), 5 ACP and 45 long Colt. They usually have adjustable sights. They have a fairly good reputation. I have several similar revolvers chambered for the 45 ACP and enjoy shooting them. In the 45 chamberings they are the lightest practical revolver available.
( edited to add) They were available mostly in stainless but some blued versions. I am not aware of any factory nickel plated Mountain Guns.