I have been building an DPMS LRT-SASS for a couple of years now and I have ran into a problem on the upper. I inserted the barrel into the receiver and slid the barrel nut over the barrel to the receiver. However the barrel nut stops at the ridge where the barrel extension meets the barrel so the threads on the nut and receiver barely touch. Its as if the barrel nut is too short. The barrel nut came with the four-rail free float tube. I have built several AR-15's without any problems like this. Any suggestions?
