It was all quite harmless until my brother turned up and decided to fashion a crossbow-type bolt out of some garden cane and bits of sheet steel, which was to be propelled by the aforementioned spud pellet. This was quite small-bore domestic gas appliance pipe, and it worked quite well. We stopped after numerous holes in the fence and a near-miss with the dog (not to mention a telling-off by She Who Must Be Obeyed). My 7-year old isn't quite at the wanting-to-blow-stuff-up stage yet, but I'm hoping he gets there soon...
D :-)