If I'm misunderstanding you Mark, please forgive me, but I've been on a third computer now, trying to get what you got, and on all three, this is the basic set-up:
1. Fall of the Rising Sun Ultimate v0.63, as downloaded from here
2. Bigger Better Protractors, which is the only other mod I have that matches yours
I'm like 99.9% certain that RR's Plot mod and the 3k Bearing Tool function as intended in the game also.
I started with wiping the Save folder to clear all my other stuff, then re-set all the screen and gameplay stuff:
started a new career:
Went in and made certain of all of my Gameplay settings etc. in the Captain's Office, then checked the equipment, of which the 50 cal machine gun is automatically there:
Checked the crew assignments, no blank spots (except the usual Damage Control Team):
Start a patrol and F12 for an external view, and all looks good:
<F> keyed my way around the boat, all function as intended, including:
... and I can zoom in with the "aimer" for "detail" work
As you can see, I'm one of the best water shooters in the USN:
I even did it all over again and bought the 20mm and went through it all over again, and I can honestly say, the clouds run away when I'm at the station:
In other words, in a mostly stock FotRSU trim on my 3 computers, no matter which way I go to the AA Gun position on a Sugar boat at Manila, it goes there, whether by the menu buttons, or the <F> key...