You need to stop the barrel from moving backward due to recoil of the shot being fired. This happened because the barrel breech did not have good metal to wood contact. This allowed the barrel to move just enough to cause a chip out at the end of the tang.
You can repair as mentioned by the others, bed the barrel, leave a gap or put a slight taper on the end of the tang, this will allow the tang to ride up instead of chipping out a piece. Bedding the breech is by far the best fix.