It's the job of Marine infantry to close with the enemy and overwhelm them with firepower.But in most cases, doing that doesn't require fully automatic weaponsin fact, they can have drawbacks.Visit Business Insider's homepage for more stories.The primary mission of a US Marine infantry rifle squad is to locate, close with, and destroy the enemy by fire and maneuver or to repel the enemy's assault by fire and close combat. This mission statement is branded into each infantryman's brain and consistently put to practical use when the grunts are deployed to the front lines.In the event a Marine infantry squad takes enemy contact, the squad leader will order the machine-gunners to relocate themselves to an area to return fire and win the battle for weapon superiority. The squad leader will also inform his fire team leaders of the situation and they'll deploy their two riflemen and SAW (Squad Automatic Weapon) gunner to a strategic areagetting them into the fight.Once they have a fix on the enemies' position, they'll call the mortar platoon to "bring the rain."At literally the flip of a switch, troops go from having a cold weapon system to knocking a fully automatic weapon, bringing death to the bad guys at the pull of a trigger.This sounds super cool, right' Well, it kind of is when you've experienced the situation first hand. We understand that having a fully automatic machine gun gives troops a commanding advantage, but when you look at how ground pounders are trained to fire the weapon system, the rate of fire nearly mirrors that of an M4's after a few bursts.SEE ALSO:Colt says it's going to stop selling AR-15 rifles to the public, but gun-control advocates shouldn't celebrate1. They can get trigger happy.For the most part, grunts love to take contact from the enemy when they are locked and loaded.When you've trained for months to take the fight to the enemy, nothing feels better than getting to fire your weapon at the bad guys. However, it's not uncommon for machine-gunners to squeeze their triggers and fire off more than the recommended four to six rounds.We'd also like to add that the feeling of sendingaccurate rounds down range is fun as f---! Unfortunately, infantrymen often lose their bearing and keep the trigger compressed and end up wasting ammo.2. Negligent discharges can be worse.Most times, a negligent discharge means you accidentally fired one round from your rifle or pistol. For a troop carrying a fully automatic weapon, the negligent discharge can be much more violent and dangerous. Instead of firing off one round accidentally, you can fire two or three.We understand that the M16 has both semi-automatic (one round at a time) and burst (three shots at a time) firing capabilities. But it's more unlikely you'll ND on the burst setting than the semi-automatic one.3. Barrel changes.Remember when we said troops can get trigger happy' Hopefully, you do, because we just mentioned it a few minutes ago.When grunts do get trigger happy, their weapons systems can overheat. To combat the overheating, troops must change out their barrel in order to stay in the fight.Which takes precious firefight time that you won't get back.4. It can lower accuracy.Machine guns are very, very powerful weapons. They can kill the enemy positioned beyond the maximum effective range of an M4 and M16. Sounds awesome, right' Well, it is.Unfortunately, since they are very powerful, when the mobile operator fires the weapon, the recoil will bring the rifle's barrel up and off target. This mainly happens when the ground pounder gets trigger happy.In a firefight, mistakes need to be kept to a minimum or people can die. Click here to read full news..