What ammo are you using? Commercial ammo comes with lots of room to spare, reloads that work in one rifle may not work in another. DPMS barrels have the tightest chambers based on reloader complaints posted on the web. Your barrel was made by an outside company and should be sent back to them with the bolt for their inspection and replacement. I suspect the barrel extension, chamber or bolt are out of spec OR your shooting reloads that haven't been resized enough to fit this chamber.
.308 rifles need a minimum of 50 foot pound torque on the barrel nut, I set mine at 70 lbs.