The first thing that you need to do, is to make a POF model with one firing point placed at the end of the barrel you want it to shot from (ussualy bottom or top) and physical model center at the point in which the gun will be attached to firepoint. The model itself needs two subobjects. The first will be the "frame" of a gun, which will not move. The second one must be a child of the first one and will be a rotating part of a gun. You will have to add "$Gun_rotation" (no quotes) to subobject proporties field in PCS2. The second subobject will rotate around it's own central axis. The firepoint will not move, the gun will always fire from it, regardless of the barrel being under it, or not.
That was making a model, now how to make it work.
First, the firepoint on the main model must be in a place in which you want the cannon to be, the physical center of a gun model will be at the firing point.
You will then have to make the weapon and assign a gun model to it.
Making weapon is easy, adding a rotating model is done by adding those lines:
$External Model File: Gatling.pof
$Submodel Rotation Speed: 52.36
$Submodel Rotation Acceleration: 50
If you don't want the gun to rotate, only the first line is needed, as it defines the weapon's external model.
The second one is speed at which your gun will rotate. To make sure it won't be firing when the barrel is not under the firing point or skip barrels, you may use this handy formula, made by Nuke for his gatling guns:
Gun rotation speed = ((1/firewait)/number of barrels)*pi The third line defines acceleration, I'm not too sure how exactly does it works, but it affects the "warmup time" of a gatling gun. The higher the value, the faster the warmup. If you set it to a value close to rotation speed, it will produce about one second warmup, which is ussualy fine.
That's pretty much everything you need to know about adding an external model to a gatling gun.
