Probably an original S&W "Registered Magnum" with a 5-1/2" barrel, in the original box with papers, etc.
For those who are not familiar with that piece, it's the first version of the .357 magnum (N sized frame),
custom built by S&W, pioneered by Colonel Daniel Baird Wesson and Phil Sharpe back around 1935.
The Registered Magnum eventually evolved into the Model 27.