I should have done this first, but I need to inform all people who are new to the Mass Effect universe, that the weapons you know today are obselete. People consider those weapons to be stone-age compred to todays weapons and armor. Here are the guns used in the current day and age.

Assault rifles are fast to fire, and have average accuracy.
http://masseffect.wikia.com/index.php?title=M-8_Avenger&image=M8avenger-png
http://masseffect.wikia.com/index.php?title=M-76_Revenant&image=Revenant-jpg
http://masseffect.wikia.com/index.php?title=M-96_Mattock&image=M-96_Mattock-png


Sniper rifles are just like our sniper rifles, except in looks.
http://masseffect.wikia.com/index.php?title=M-92_Mantis&image=Mantis_Sniper-png
http://masseffect.wikia.com/index.php?title=M-97_Viper&image=Viper_Sniper-png
http://masseffect.wikia.com/index.php?title=M-98_Widow&image=Widow2-png
http://masseffect.wikia.com/index.php?title=M-29_Incisor&image=Incisor_Sniper_Rifle-png

Shotguns deliver a deadly punch at close range, but are useless at a distance.
http://masseffect.wikia.com/index.php?title=M-23_Katana&image=Katana_Shotgun-png
http://masseffect.wikia.com/index.php?title=M-27_Scimitar&image=Scimitar_Assault_Shotgun-png
http://masseffect.wikia.com/index.php?title=M-300_Claymore&image=M300Claymore-png

Pistols are the classic sidearm, and are used by all classes.
http://masseffect.wikia.com/index.php?title=Heavy_Pistols&image=M-5_Phalanx-png
http://masseffect.wikia.com/index.php?title=Heavy_Pistols&image=X3c_Predator-png

Machine guns are fast, but have low accuracy.
http://masseffect.wikia.com/index.php?title=Submachine_Guns&image=Tempest-png
http://masseffect.wikia.com/index.php?title=Submachine_Guns&image=M12_Locust-png

There you go, for the sake of conveniance, both types of rifles collapse when not in use, to make it easier to store them.