Well, you could have been more specific! You could always tell the mod maker to rename one of the weapons, since it is his/her fault for doing it wrong (it is incredibly simple to do, if you just look at what BIS did!).
Anyway, you could do a nearestObject on the ammo type used and then use "_helo worldToModel (getPos _ammo)". If the position is left of centre in the model coordinates, then it is the left gun. To the right of the centre it is the right gun. This assumes, of course, that the two guns don't have overlapping arcs...