The sand is iron, chidori nagashi should be able to travel through it.
The heart
(CORE) is the only living substance in sasori's body. The core to the sharigan would be showing the most chakra which would obviously give a hint to sasuke that the focal point to sasori's demise would be the core. Not too mention when sasori using his main body he takes off his robe[
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]. The appearance of the core will only make it even more obvious to sasuke that he needs to land a vital hit on that particular spot.
Iron shower? Are you referring to iron sand drizzle?
The fact that sakura doesnt even have speed feats comparable to sasuke which even suggest that she would had been able to evade the sand drizzle yet lady chiyo was capable of intervening in time with her puppet to save sakura[
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]. Taking this into account Sasuke will have no trouble evading the sand drizzle with his immense shunsin that the DB describe to be god-like.