I have been using those settings for the deck gun for some time now.It is an accurate loadout from what Uboat.net says.Thats why I changed them....since Uboats did not carry Starshells or Armor Piercing rounds.
I originally did this after reading one of Sailor Steves posts about him using these settings..so this has been around for awhile now.Why this is not used in RUB I dont know as this is a more realistic loadout then what the stock game gives you.And as you state also makes you have to load the first shell into the gun beofre you can fire it.
Heres the thread...
http://www.subsim.com/phpBB/viewtopi...light=deck+gun