I examined this gun for about ten to 15 minutes at a gun show in San Angelo a year or so ago.  I was amazed at the good condition with brass small parts, sight etc.  The quality of the work was very good on what appears to be a designers model to exhibit the concept, especially after I dropped a light down the barrel and confirmed smoothbore.  The Bullard buttplate was in very good condition and was nicely attached to the buttstock.  This is a very nice gun but of very little practical use.   
James

There are several side plate stevens rifles with brass frames that are documented prototypes in the factory. 
Most likely, brass being easier to machine, it was preferred for trying out new ideas. 

Such changes in the design were incorporated into production without any announcement or fanfare in the side plate years.

I think this rifle is another such shop model. I'd like to see beneath the side plate to see what changes were made.

Regards,
Ron

Otis Wyman Horr (1828-1900) was a machinist & stockmaker who worked for Stevens from the early 1870s thru the early 1890s.  He lived on Fuller Street in Chicopee Falls.

Thanks, Chuck. I appreciate that coming from a master gunmaker.