Thank you for that. Yes I have that manual. I had not gone to look at the passage on cannister for some months. I would fire a gun across white sand and you would be able to trace the paths etc.. from this.
The other method would be to put up linen banners across the path from about 50 yards. Closser than that may well have problems with the blast and fire from the deflagration of the charge. Remember about a third of the charge is lost either through the windage or vent.