Yeah, see, that way a chaingun, or minigun, is constructed, is by linking multiple barrels to a rotary assembly, and spinning them as the extremely high rate of fire rounds are coming through. The purpose of the spinning barrels is to allow the barrels to cool in between rounds, so you don't end up with a pile of slag after ten seconds of firing.
Now, take an assault rifle, look at it hard, and figure out how to do all of that to it without just saying "to hell with it" and buying a minigun.... Most armorers are going to slap you in the face with a howitzer before they will try to turn an assault rifle into a chaingun.
