As I understand it, guns in AH are coded by type, e.g. an aircraft Browning .50 uses the same code, be it in the wing of the P-47D-40 or the ball turret of a B-17G. If you have tested the gun in one place, you have tested it in all places, excepting rate of fire with interrupter gear. If, for example, the tail gun on the B5N2 is the same type of gun as the guns on the D3A1 then you have already tested the damage per shot. Rate of fire can be tested in the air just fine.
The problem is this...the gun on the Kate is also one of the guns on the Val...however...you cannot separate the guns on the Val...there is no secondary fire...
Thus the type 92 is not a stand alone weapon on the Val...its linked up with the 97...
The only place in the game that the 92 exists in a stand alone config is the tail of Kate
Its probably the only condition (at lease so far I have discovered) like this.
There are some gun packs like the pack on the A65 that has the 13.2 Type 3 that exists on no other airplane in the game...and is linked with the other machine gun..and thus cannot be tested at all...
All in all their will be a few holes in the data base and it appears as if their is no work around for these atypical conditions
Oneway
edit: your correct ROF can be done once airborne...but the ammo load aggregated weight and bullet weight calculation cannot because of the fuel burn...unless I do dry fire runs and then live fire runs...that is a pain the butt I do not want to do unless absolutely necessary....parking in the hanger and blasting away with engines off is the slickest and quickest.