Quick Question About Urgot

I like theorizing about new champs to play and what builds will be fun. I'm looking at Urgot and considering trying him. I am reading his abilities, and it looks like his W, "Purge," reduces on-hit damage by 50%. Does this mean if I have my W activated, then my knee shotguns will do 50% damage? It's an important question, because it would affect when I use certain spells on him and when I choose to avoid using those spells.