Godfrey if you want to make a bang on cue with a bit of flash etc, you need a metal gun barrel to take the power of the explosive, i suggest a light bulb with the glass removed leaving the filament exposed, wire up a spare servo so it drives a wafer switch to put a battery across the terminals of your light bulb if you fix the bulb with the filament upa gun barrel, and is fixed most firmly in place, it is a simple matter to muzzle load some of the innards of a firework(not too much now, or you’ll blow the transom off your model.After loading a very small amount of explosive into the barrel, you need to contain it so that it releases with the required bang. This is where a bit of oasis foam comes in handyThe oasis will be blown out your gun barrel with a most satisfying bang, and being a very brittle substance on cotact with the outside air will break up into extremely small particles, not big enough to do any harm to anyperson nearby, or the retired colonel’s marblehead alongside, The only harm might be that the old colonel has a heart attack thinking he’s back in the crimea. There was a bit of common sense in one of the other replies you had, that was to get some insurance, but having given you the method, I do say earnestly keep the quantity of explosive within  reasonable bounds, I dread to think of a scale reproduction of HMS Hood getting a german shell right in the magazine. Just think of all the work you have put in to build the model.  OOps I nearly forgot, you need to use the oasis like the wadding in blunderbussespush a piece of oasis ito the barrel just after the gunpowderso that the gunpowder is held firmly against the bulb filament, but not firmly enough to break it or it wont go off. the tighter the seal, the bigger the bang. If you’re selling tickets, I’ll have one as you can guess, I love it.!

Good luck……………….Mike D  

 p.s. oasis is the  green foam ladies stick in the bottom of vases to hold flowers upright in the water you can buy it in flower shops.                          Gunpowder contained in a strong container is called a bomb