Perhaps it might help if I explain my thought process?
Having cleared the first hurdle of the FAC itself and leaving aside the issue of sourcing the parts to build a live gun, I need to work out the best solution for the charges. The most obvious is the use of pukka L46A1 blanks, but they will undoubtedly be very expensive and probably complete overkill. I don't want to shatter windows or burst eardrums just for effects at a show. The next approach, which is what I suggested as part of the FAC application, is to reload used cases with black powder. Another solution would be to find a suitable electrically triggered pyrotechnic and build it into a modified case.
So at the moment I'm investigating to see what other people do in similar circumstances, hence my question here. Other sources of information are Edinburgh Castle (the 1 o'clock gun is a 105mm Light Gun) and re-enactors such as the group who fire the 4 inch guns on HMS Belfast. And of course, closest to me are the group who fire artillery at Fort Nelson.
Does that make sense?
Andy