How was David feeling on pages 71 -72, when he said " i shot up the entire box of bullets" and when he shot the magpie ( bird)? Why?

Clearly this shows frustration on David's part; he is not a violent boy. He shoots the bullets because he is aware of what is going on even if adults think they are hiding it from him. They are not aware of David's own understanding of sexuality as well as his sense of futility over what has happened with Uncle Frank.