"Have you guys ever seen a Rubin rifle? it was a rifle that was converted to a 12 ga shotgun.... it looks early 1800's my dad thinks it was a fairly common conversion a long long time ago."

The only ones I am familiar with were the Swiss Schmidt-Rubin straight-pull military rifles, and I have never seen nor heard of one being converted to a shotgun. After WWI, a great many German Mauser military rifles were converted to cheap bolt action shotguns in Germany by various shops for export. Maybe that is what you are thinking of. They were once very common, but I haven't seen one for a long time.

Read more about them here: http://texastradingpost.com/militaria/geha.html