Talk:Equipment/@comment-155.69.203.4-20140206105104/@comment-24473957-20140206113418

http://livedoor.blogimg.jp/lovelive2015-kantai/imgs/1/c/1c5f7dd1.jpg

this was from the official interview.

In simple terms, armor penetration is calculated each time you attack in shelling phase. Type91AP appears to affect armor penetration.

So technically you will do higher damage using AP rounds against more armored targets.