I like this

is this uncommon considering Magmatic Insight, though that might be because the card could mana screw you.

I'd forgotten about Magmatic Insight. I think it's in uncommon in part because of the fell bad of discarding as a cost and the mana screw. Duel decks are a bit more of an elevated product then origins though and this won't mana screw (quite the opposite it can mana fix), so I could see this going either way.

­Wild Guess and Tormenting Voice are common so this seems fine to me.

contesting with Junker Goblin

I like the card.

Putting it in a common slot is cheating though. This is Magmatic Insight except discarding an artifact sets up more ridiculous things in this deck than discarding a land ever will.

Counterpoint being that discarding a land is relevant in any deck making it more valuable while discarding artifacts is deck specific.

That and discarding a land as mentioned above has more mana related fell bads.

I think in a duel deck this is the type of effect that makes sense as a common, as opposed to a drafting environment of Magic Origins.

The first point is actually a point against it being at common. You don't want oddly specific cards to be present at common, especially if the card is not necessary for the archetype and is unusable for other archetypes.

­Shrapnel Blast comes to mind as a point of comparison. Even in sets loaded with artifacts it is an Uncommon

I agree with SecretInfiltraitor and CasualR here, what could we remove to make this uncommon? And if nothing then lets free up the slot.

­Mechanical Kavu and Improvised Bomb seem to doing the same thing. I'd stop improvised bomb and put this card there.