I have a 7.62 and 556 pistol 10 inch barrels that are currently sharing a lower anderson reciever. when I first shot both barrels would fire the round, but would not eject the casing and would try to load another round. I changed out a 4.7 ounce buffer for a 3.0 oz..it also did not inject the round properly but did not try to jam the round as hard. the 556 tried to load the new round in and the 762 barely moved the next round out of the magazine....any tips or thoughts in what's wrong??