I don’t believe the quoted statements below are correct. Stainless
alloys are primarily iron, with large percentages of chromium and
nickel added along with a few other metals in smaller percentages
depending on the exact alloy you are talking about. Chromium oxidizes
to form a protective film on the surface of the metal, forming the
primary protection of the iron in the alloy from rusting. This does
not make the metal rust-proof, merely very rust resistant, some
alloys more than others. Stainless typically rusts when something
breaks down the chromium oxide film or depletes the chromium content
at the surface of the metal. This can occur via several processes,
typically via chemicals or by high heat (welding, soldering). Also,
some stainless alloys are magnetic.
That being said, I’ve never had my stainless shot rust. It has
discolored slightly over the years, so it isn’t quite as shiny as it
once was, but it still seems to work just fine.