Thanks Armando.
After the crew explained how and what they were doing, they gave a count-down to firing the shot, so I had time to get ready and when they got close, I used the drive to take a sequence of shots, hoping to catch the muzzle flash, which I was lucky enough to get. However, while doing that there was a bit of camera drift to the right, which is why the figure on the left is badly cropped.
Robert