I forgot to say that if you want the ammo in the gun from the beginning, you have to put a mag in first. So it would go,
addammo ~ addweapon
Ok, for F14 etc, you'll have to check the readme which came with the addon. However you may well have noticed that few addon makers think to put the weapon names in. I don't think it's done on purpose just not thought of.
You're gonna have to e-mail the builder and ask them for it. You shouldn't have any trouble, but then you never know.
There is a simpler way of doing it by opening up the file. Unfortunatly I don't know how to do it so you'll have to hope someone else can sort you out there.