Rick,
the issue is that virtually all of the load expanding this area of the chamber is being held by the little remaining web identified by the red arrow. The web identified by the yellow arrow isn't of much help in carrying the load if at all. It may even be worse than that. The load may fail the web between the chamber and the gunsmith hack's hole and then cascade thru the web to the original hole then thru the even thinner outer web between the original hole and outside.