This is something called 'bloom.' Basically, imagine that after a shot, the accuracy cone of the weapon widens and then decreases back to its original volume. In that time when the accuracy cone is widened, it's less likely that you will hit your shot. This means you must pace your shots if you want to be accurate with hand cannons. Some hand cannons can shoot faster than their bloom resets - Hawkmoon is one of them. You have to use the weapon correctly for its best results, which means you have to strike the delicate balance between firing it quickly and giving it time for the bloom to not make you miss. Just for your information, bloom is not something many players are a fan of. It was very controversial when Bungie implemented it in Halo but it is actually a very good mechanic when done right.