Upgrading the porter's x2 ray gun?

Alright im not sure about this but its driving me crazy since i dotn have call of the dead yet and i cant test this out on my own. My younger brothers friend said that its possible to upgrade past the first upgrade so in example ray gun -> porter's x2 ray gun -> ?. With each upgrade costing more than the last so in order it would go 5,000 to 10,000 and so forth. He said that the ray gun at level three is black and shoots purple bullets. Now im pretty sure its a hoax but i wanna know because if its true ima sit at the game forever until i get me some glowing purple balls to shoot in romero's face. then if its not on call of the dead i was thinking it could possibly in anihilation because treyarch said the map is tightly packed so to make it easier with these harder to kill special zombies and faster and stronger zombies they might have added the additional upgrades just at the cost of more points to even the odds for the players? I'm not sure just wondering