My FHP 28 was in the S192xxx serial number range. The guns are
marked, I think on the butt, as being FHP. Mine was a 5" gun, and I
think all of them were 5". S182xxx is too early, and its the wrong
barrel length. FHP also had some 5" model 19's in nickel - seems
they liked that barrel length.
There were a few - very few - 4" brushed nickel 28's, but they are much
later. Serial number range is N38xxx .
Its always possible that there were other batches of nickel 28's, so
a letter is probably worth it.
Regards, Mike Priwer