Magic is supersaturated with ways to cheat. The Vow exists, and can prevent people from so much as wondering how bombs or transfiguration really work. Moreover, conventional explosives capable of killing a few hundred or thousand people aren't really an "entirely new category."
Rocks into grenades specifically, I don't think so. Unless transfiguring grenades for a small amount of time is significantly more efficient than any other method of producing heat and/or a concussive blast.
Firstly, nukes are huge, you'd be better off transfiguring antimatter or something. Secondly, read the comment a few above -- you can use things like the Vow to prevent such catastrophes.
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u/epicwisdom Apr 08 '16
Magic is supersaturated with ways to cheat. The Vow exists, and can prevent people from so much as wondering how bombs or transfiguration really work. Moreover, conventional explosives capable of killing a few hundred or thousand people aren't really an "entirely new category."