Patent Models are very collectible and rare. To learn more about the history of Patent Models in the United States, and about the destruction suffered after two fires in the US Patent Office, see the following article by Donald W. Hogan. Unwanted Treasures of the Patent Office. American Heritage Magazine, Volume 9, Issue 2, February 1958.
This Barnes "Swan on Swan" slug iron was auctioned on May 1, 2016 and sold for the winning bid of $6,000.
Of special interest is that this is the original patent model. The attached note states it was found in the debris of the Patent Office fire of 1877.
The auction information and images are shared courtesy of William J. Jenack Auctioneers of Chester, New York. This auction was broadcast live on liveauctioneers.
See also Irons-Slug/Box Irons for another Barnes "Swan on Swan" Slug Iron.