Sasori is a genius level ninja and was partnered with Orochimaru before.. I do not think at all he'd seriously start a fight with him using hiruko..that's a pure underestimation...
Kusunagi can't be used once iron sand is out... metal objects are all under the control of the puppet due to its magnetic field
Sasori
WILL start in hiruko. People who always claim sasori will whip out 3rd kazekage right off the bat just sound foolish. Hiruko eliminates
EVERY disadvantage of a puppet master. He won't leave hiruko to open up himself for exploit. Hiruko is infact his best cover because it offers so many traps to poison with, and superb defence.
Orochimaru takes this. Manda smashes through hiruko and 100 puppets. Sasori's poison would most likely not even affect orochimaru since he's trained many of his pupils in poison resistance and has even experimented on his body to the point where poison flows through his blood in his white snake form.
EDIT: To the people stating that sasori would make a poison that affects oro; how? How would he possibly know what poison would affect oro? Oro wouldn't come up to sasori and hand him his actual blood. Even if oro were to cut himself, that's not even oro. You need his white snake form's blood to even figure out what he isn't immune to. The fact the man has made blood course through his veins is strong enough evidence that sasori's poison most likely own't affect him. Infact, poison fights poison...