MC has been a Porter for years and doesn't understand the concept that Full-Auto means less accuracy and a faster rate of eating through your ammunition.
@saitoh514, I agree, but MC isn't very smart. His skill set, IMHO, makes him more of a close-range fighter, but he hasn't seemed to grasp that concept yet.
@Syanalassa, the bow, and arrow didn't do anything against the sinkhole insect monster so it's not necessarily true that melee weapons are better. It appears the weapons are based on hunter skill sets. Those that use Power strike tend to favor melee weapons while other hunters favor guns because they can amplify the ammunition like the MC can in some way.
Still, like saitoh514 pointed out, bullets seem to only do something when the author wants them to. These characters supposedly have the training and have been fighting these monsters for the past decade or so, yet they still waste bullets on monsters like this. The bullets don't even seem to distract most monsters half of the time.