Hey guys,
All of your responses make complete sense.
It took just a minute to go online to find a PDF of a Rossi Owner's Manual (
http://www.rossiusa.com/pdf/Rossi_Manual_Rio_Grande.pdf ) and they say
2. The use of reloaded, “remanufactured”, hand-loaded, or other non- standard ammunition voids all warranties. Improperly loaded ammunition voids all warranties. Improperly loaded ammunition can be extremely dangerous. Severe damage to the firearm and serious injury to the shooter or to others may result. Always use ammunition that complies with the industry performance standards established by the Sporting Arms and Ammunition Manufacturers Institute, Inc., of the United States, (SAAMI) or the equivalent from other countries.
but they give no real reason. I think that it's just lawyerly boilerplate ... they probably use the same comment for every firearm they make.