I know quite a bit about the V40 story. I was involved in its being taken out of service. It was purchased because some wizard of a staff officer who figured out that, if a grenade weighed only 1/4 lb, a soldier could carry 4 of them as easily as he could an M67 (the US grenade at the time) which weighed 1 lb. Grenades are only effective if thrown into a trench, bunker or some other enclosed space. If someone has four chances to hit his target, the probability of doing so increases dramatically.
The first problem with this theory is that the practical range of a handthrown grenade is not much more than 30 metres. If you are that close to an enemy that is trying his very best to kill you, do you think you are going to get a chance to throw a second grenade, let alone a third or fourth?
The second problem is that the target effect of any high explosive, fragmenting device - bomb, shell or grenade - increases exponentially with an increase in the weight of framenting metal and the weight of explosive driving it. For example, if you double the weight of an HE fragmenting device, you will get perhaps four times the target effect. That's why hand grenades all weight about 1 lb - it's the most an average man can throw, bending his elbow. (The big exceptions, of course were the No.5 Mills bomb or the No. 36 that replaced it, which both weighed about 1 1/2 lb. They had to be thrown with a stiff arm much as one would throw a cricket ball.) The V40 weighed only 1/4 lb so was not likely to be very lethal.
At that time the V40s were all held in war reserve. What a dumb idea! If we went to war, our soldiers would be given hand grenades they had never seen before. We decided to start issuing V40s for training and both they and the M67s were allocated half and half. Then the trouble started.
The first incident was when we a V40 explode in a soldier's hand on a grenade range in Germany. He lost most of one arm and part of his other (mainly because of a trained first aider being on the scene) but survived. I have never heard of anyone else ever surviving when a grenade exploding in his hand. We thought we should get rid of the V40 then because it was obviously not effective but the ammunition folks objected because they had just spent a lot on a completed a contract to replace all the detonators and didn't want to waste all that money.
((I've got to tell the rest of this story in another pot because I can't fit it in here. ))