I can’t tell you why there is a hole in the mag plug. Mine has no hole. But I will say that my east Taylor heat shield had flats between the rows of holes. Makes sense as the weaker steel [where the holes are] will bend before the solid steel will. I made an anvil out of a piece of oak board and used a socket and rubber mallet to round out my heat shield. Used my table saw and fed the wood into it at an angle to get a long half circle. Sanded it a little. Then used the socket to gently round it by forming it to the curve I’d cut.