I own 2of these upper ass,ys , the two screws are to set the correct oal length for the bolt carrier assy to fit correctly in the upper assy.Insert the bolt assy into your upper making sure the front is flush to the barrel collar face, the rear of the carrier assy should be flush and square to the rear of the upper receiver ,if not adjust the two screws in or out as needed to make is so. These screws will not move on there own once adjusted as the carrier is locked in the upper when the upper and lower are together. My uppers came with a note saying that they should only be used with lower assy's using a stock hammer, trigger and spring system.If non stock fire control parts are being used, erratic functon and firing can result. Hope this helped if not disregard and send the upper back to DPMS. I'm Sure they will take care of it for you.