Powder Keg

I was using the practice tool today for Gangplank looking at some different options. Now I'm fairly new to Gangplank, but I have noticed that Powder Keg has no AP or AD scaling according to the thumbnail etc, even on other sites. What I found out today is that even though there is no AD scaling listed it does in fact scale with AD. Not all that much but I did notice If I stack only the BF Swords that my damage does go up at least 100 damage on the target dummy.

So I was wondering if anyone knows if is there some kind of hidden math equation for Powder Keg?