What are the problems with normal light weapons? eg. rifles, SMGs, Machine Guns, etc.

I need problems with them. For example, not being able to shoot underwater, running out of bullets, things of that nature. I don't necessarily need answers to the questions, and in some cases there won't be an answer. Can you guys come up with some problems for me?

Pretty vague, can you be more specific?

Heat dissipation. Typically the lighter the weapon system the quicker it is going to warm up. If you want sustained fully auto you need a barrel with some weight to it otherwise it will burn itself up if your not careful.

it's vague on purpose, overheating is a perfect example of what kind of thing i'm talking about, thanks. any more?

That's why I always humped a skrootch gun.
Cunning, those extraterrestrials.

Muzzle flash,muzzle climb on automatic,heavy weight of ammunition,not enough stopping power of ammunition,over (or under)penetration of ammunition,loss of accuracy of ammunition with increased range or decreased length of weapon,loss of mobility of weapon with increased length of weapon,loss of muzzle velocity with addition of silencer/suppressor,increase in weapon noise without previous,increased weight with heavier barrell,decreased life of barrell with lighter barrell,loss of reliability with cheaper production costs,PRODUCTION/DEVELOPMENT COSTS!!!............. the list is almost endless.

Need for frequent cleaning.

Now how often do you hear of a person fighting under water with firearms. Most of the modern weapons once they have been battlefield tested and have had the faults corrected will work fairly well any where