In a similar vein but with thunderflash. The standard way that DS demonstrated the power of these to recruits was to strike the thing, cover it with a tin helmet which would fly 50 feet into the air when the device went bang. One Cpl decided a better demo would be for him to stand on top of the helmet and the ensuing force would lift him a couple of feet, of course matters such as interia, force, Newton's laws of motion etc. all contrived to break one of his ankles at boom time, which, to be fair, are not the kind of matters that typically preoccupy DS. Anyway he was carted off to get fixed and presumably never tried that trick again, although another DS Cpl lost a finger or two while demoing (badly) something with a thunderflash.
It's always A DS Cpl who dream up these kind of flawed stunts isn't it? (and long may they continue) I wonder if our on set armourer in this case was a former DS Cpl?
If I recall correctly, the "stick a thunderflash under a helmet" thingy went out of the window with the introduction of that GRP nylon thingy trying to masquerade as an American PASGT helmet. Mainly because it'd explode into a shower of high-velocity plastic shards and wipe out the entire lot of gormless recruits and the equally-if-not-more-so DS staff all in a oner.