A friend of mine runs master transmuter in a deck with several cards that say "whenever you cast an artifact spell". I was under the assumption that playing the transmuter's ability would not be "casting" when you put the artifact from your hand to the battlefield, because it is part of the ability and not a spell. He argues that it's coming from your hand so it must count as a spell. Would one of you fine gurus clear this up for us? thanks.
You are correct. Casting a spell is to put that spell from your hand (usually) onto the stack, paying for any and all costs associated. Master Transmuter has an activated ability that simply puts an artifact onto the battlefield from the hand; it does not cast it, and will not trigger any triggered abilities that say anything like "whenever you cast an artifact spell".
Quote from Comprehensive Rules »
601.2 (excerpt) To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect.
master transmuter's ability