While I don't have a pic of the UR shotgun, it should be easy for you (the devs, not necessarily the players) to validate.
I upgraded the shotgun to Epic, and the stats are the same as the UR - no damage increase, no mod added, ect:
http://imgur.com/CpPnex4
I was expecting/hoping for the normal [Dm/CrH] mod or something the other Epics get