I have decided not to pursue implementing a custom Foundation listener to trigger my code alongside its damper onYield code.
My current implementation, although not ideal as every weapon that hits anything will trigger it, 'just works' and it would not be worth the time it would take me to learn this Foundation implementation and adapt my code.
This is not to say I like half-arsed attempts at doing things, I'm just being realistic with the real world time being put into it and the outcome.
Again thanks for all your help.