Let me give an example of something that may help, related to index numbers in weäp resources.
If you take the time to examine the weäp resources of EVN, you will find that there is a separate weäp resource for the Wraithii Cannon for every faction and mission string that uses it. However, there is only one outfit resource of Wraithii. All the weäp resources are set to AmmoType of 17, which I think is the index number of Wraithii. This allows all of the weĺp resources to use the same ammo.
However, this does not work so well in plugs. In beta-testing Nebula (which ended up lame anyway, because of file corruption... I still have my stable dev files, and I should post them somewhere...), I found that the Federation Special Forces Wraithii outfit would not display how many Wraithii my SF ship already had, and buying Wraithii did not increase the count of available Wraithii. The weäp resource had AmmoType of 17, just like the stock Nova, but it didn't work. Finally, I changed the AmmoType to 248, Which was the index number of the weäp resource (Index number = ID number - 128). The Weäp resource ID was 376. Anyways, this is what I found out from the EV Bible to explain this.
Quote
AmmoType: What kind of ammo the weapon uses:
-1 Ignored (unlimited ammo)
0-255 Draws ammo from this type of weapon. (Usually, if your Hector Cannon was of ID 131, you'd set the AmmoType to 3 so it'd use Hector Birdseed Pellets or whatever. However, you could conceivably set it to use ammo from another weapon's supply by setting the AmmoType to something else.)
-999 Ship is destroyed when weapon is fired
-1000 & below Weapon uses abs(AmmoType+1000)/10 units of fuel per shot. (example: -1005 = 0.5 units per shot)
As I interpret this, you should always set the Ammotype of a weäp resource that uses an outfit resource for ammo to the weĺp resource's index number. As the EV Bible states, if the ID of the Hector cannon is 131, you would set the AmmoType to 3. To cue the correct outfit for the ammo, you merely need to set the outfit as ammo for the correct weäp resource in the ModVal field. Needless to say, this fixed the Wraithii bug, and the outfit worked smoothly after that.
I'm not sure if this is exactly what you want, but it may be useful if you ever find that your ammo outfits aren't working right.