Firearms Skillgroup
* One-Handed Weapons (pistols, mp's) - small, easy to conceal, low dmg
* Two-Handed Weapons (longarms, assault rifles, machine guns) - huge, not concealable, high dmg
* Ballistic Weapons (rocket launcher, grenade launcher, probably mortars) - you know them
Yup, i put heavy weapons in just as well. There is really no explanation why an expert with an assault rifle should not be able to fire a machine gun (it's the same just bigger).
This is how different weapons are categorized today as well. The difference is in how they are fired. You can get either pistol or rifle training - sadly never heard of a ballistics course though