Yeah, I like this a lot. I know it sounds like the dm is giving the player a lot of power here, but hear me out - yes. And why not? For a spell you have to be within 30 feet of the target to pull off in the first place, and you also wanna try and potentially get advantage for a sneak attack or...
Everyone here keeps saying no, but I actually disagree. I believe if you fire magic stone from a +2 sling, it ignores the 1d4 of the sling but keeps the +2 since it was an attack roll made using the sling. In the same way, steel wind strike uses the sword as a material component in the spell...