OK, so I have a dpms sweet16 bull barrel rifle. I ordered a troy trx standard rail to put on the upper. When I went to reassemble the upper with the new rail I could not get the barrel nut on. It went easily over the front of the barrel but would not go past the section where the gas block is. I called dpms and troy to get exact measurements to see what is going on. DPMS says that the diameter of the barrel .936 and troy says the inside diameter of the barrel nut is 1.043. What gives? Any help is greatly appreciated. I attached a pic of a dpms barrel(mine isn't fluted) to give you an idea.