It is no design flaw and I think you will find that is the design that is used by most manufacturers for that type of muffler. For example it is used by all the current OS two strokes with mufflers and it works very well with them.

I don,t use GMS engines but perhaps it is related to the hardness temper of the bolt and the thread count used for the threads. If you drill out and depend on that tiny metric nut you will likely end up with worse problems and losing the tailcones in flight.


John