Mine too, I have a companion that uses it a lot. He has the Laser RCW and Vance's gun but he usually uses the sub machine gun. The only thing I notice is it uses a lot of ammo! At least my companion uses a lot of ammo.
Kind of svcks that Primm Slim doesn't offer any dialogue when you bring it there.
I thought I read somewhere that bringing the machinegun back to the Vickie and Vance Museum was a quest that was never finished being written when the game was released.
At some point I'm sure a fan will write a mod for this "missing" quest. You will be able to do it then. Just keep your eyes on the growing list of mods for New Vegas.