Different people has different play style so it's vary. However, for me I use level 68 guns on caio duilio 1915 with no armor just 0.2 belt and bulge until you lose a knot. The rest is up to you how many shells you want to load. Some people vary that they use level 73 Gun on caio duilio 1915 because of more range slower reload than the level 68 guns. Hope this helps you.
