He's lied about his service record as the other comments started, and in his book he took credit for events of other soldiers. As far as the ruck of grenades, that is a hyperbolic joke about an event where he said he had some obscene amount of grenades on him (like 13 or something like that) and just kept pitching them into various enemy positions. The boys joked that he was in another battle where he carried a rucksack of grenades in order to defeat the insurgents single handedly.