It is your great-grandfathers rifle, so yes it is rare.
The rear sight is Lyman #6 which apparently was a factory option at the time.
http://www.soldusa.com/rainworx/detail.asp?id=47917
Need more pics..........end of magazine and last section of lower portion of barrel..........Looks like mag was cut, in which case take 'er out and hunt with it as it has zero collector value, and is a great deer cartridge. Or just hang 'er up 'cause she was granddads.........




























