if david and mr.morrison had marched over to the lynch moband fired guns,what would have happened

Unfortunately running out of bullets would have been the least of their worries. The civil rights movement was a long way away. Blacks who fought back endangered themselves and their families. David and Mr. Morrison would most likely have been killed. Firing a gun at a lynch mob would give the mob implicit authority to do whatever they wanted. Just think of an atrocity and the mob would justify in the name of "justice". .