My normal, when testing the Tenko and running my DIAS, is to switch uppers after four 30 round mags or after a 100 round Beta-C. But I do that so I am not abusing the upper and it is cooler so that I don't get burned so easily. I can dump two Beta-C mags in a row, but it front lug of the upper will get to 260 degrees. That gets the front pin pretty hot. I also feel that the hotter the barrel, the faster it will wear. So changing the uppers more often has them last longer.You're basically asking the same question an m16 owner asks, except that this gun should be actually cooler because it runs open bolt. I think I remember an M16 owner saying they switch uppers after three mags. Since you only have one, you'll have to just wait I guess.
Don't blame the upper, there's tremendously more energy in these rifle rounds than there is in a 9 mm round.