What background info do you have to support that it is a Ruby ? Where did your Granddad acquire the stone ? Just looking at the photos you provided, one could say that this stone could possibly be in the Garnet family, or even a variety of Tourmaline known as Rubillite. You should have it tested to confirm what it is first, then you can better judge its value or rarity.
Good Luck !
Response to Swarnava post 28 Aug 2015