A little help for the future:
Go to Game Info on the site menu, click components, and click the rising sun. The information is outdated in a few areas, especially if there's been a recent change, but is mostly accurate. Still, it will be more up to date and harder to confuse yourself with than forum posts from years ago.
The 18.9" are level 100. They have been for as long as BB5s have been around. The 110 guns are the 20.1"/45 Type 98A. They also have always been that way. The 110 guns are inferior to the 100 guns in every BB5 that has them. Never use a level 110 gun. Ever.