for the detent, have the bolt installed in the fully closed position, then use a center drill to locate and start the hole. Next get a drill that is a few thousands smaller than the diameter of the detent ball, now drill through the breech, and just into the surface of the bolt. Next retract the bolt, and repete with same drill. next remove bolt, and redrill hole in breech the tap drill size for the thread. Everything should line up perfectly. hth.
