Err, you could just use
MachineGun30A10
which is basically 4 shots of a helicopter's cannon in 1 burst.
What are you talking about? With the civvi, a script or something?
BTW: The vulcan ammo would be from a big arse gun, I haven't seen too many infantrymen carrying 30mm cannons.
Plus the gun has a small area of effect so if a unit is close enough he'll get damaged when it looks like the bullets/shells are missing him. But try the script I suggested. It provided a nice MG randomness effect to my D-day look alike.
Edit: Oh yea vulcan ammo is like "Vulcan" or something. But it seems very similiar to the A10 cannon.
Edit2: ok disreguard my first edit, bedges has it. Sometimes they have captials too so.