Most likley an assembly number.
45 Smith and Wesson
smith and wesson.
A shotgun made for Smith and Wesson, sold under the Smith and Wesson name.
No engineering changes.
Enhanced
The Wesson part of Smith and Wesson.
Standard Catalog of Smith and Wesson
Horace Smith, Daniel Wesson
Smith and Wesson will tell you if you call them
Smith & Wesson was founded in 1852.
In this forum's context, Smith and Wesson, Target Sights.
No engineering changes have been made.