My son assembled a 308 using the DPMS standard parts from different manufacturers (LR-308). It has failure to feed after the first round. It has an 18" barrel, mid-length gas, adjustable gas block, rifle buffer tube, 5.4oz rifle buffer and rifle length spring. When charging with the charging handle, it fires fine, cartridge ejects at about 2:00-3:00, and it feeds the next round, but the trigger won't function and it feels like it is not going into battery. Forward assist doesn't do anything as the BCG does not have the ridges on it. Pulling back the charging handle ejects the bullet and feeds another one, and the cycle repeats. We tried adjusting the gas and tried a 3.5oz carbine buffer, but it didn't change. When loading only one round, the bolt locks back on an empty mag, so I'm sure it has enough gas. I am thinking it needs a stronger spring?