After a bit of contemplation, I have another theory that I believe makes more sense and matches my observations. Please let me know your thoughts?
The last time this happened, I blew a small hole through a thin-wall FW/FG airframe, not just a crack. At that time, and up until now, I thought it was because of the hanging BP holder ricocheting off the inside of the airframe.
I just inspected and cleaned the inside of BF airframe, and I noted a very dark and concentrated scorch mark around the split. I also clearly recalled, that when I ground tested these spent diabetic needle caps, the intensity of sound was far greater than anything I had experienced before. It was so loud that my ears rang for about ten min. I have done a lot of ground testing, and nothing has compared, even with twice the load. At the time, I just passed it off.
Below is my new theory, which I am sure will be fairly obvious to some of you. The base of the hanging charge was likely facing, as well as up against the inside wall of the airframe. Combining this with the rigidity of the cap, which probably focused the blast, it resulted in what you see below.
Below are some pics of the spent hanging charge cap.
As you can see, the cap survived both the expanding hot gases and the heat with nothing more than some minor discolouration.
This brings me to my plan to resurrect the original BF.
Instead of fixing it as a flight-ready airframe, which would necessitate some body work inside and outside, I am just going to make it visually "fixed" and leave it as a static model. I am going to repurpose this nosecone, which is not the original and make use of some left-over Mac 54mm CF airframe. I also have some perfectly sized CF plate that I have been looking for something to use it on.
This will be a one-off custom all CF BlackFly that I will leave natural, just a thin layer of epoxy to cover it and bring out a shine, and a very subtle black on black BlackFly logo with red eyes.