Making a kinyan on hefker items on Shabbat

Question

Is it possible to take possession (make a kinyan) of items which are hefker (ownerless) on Shabbat?

I know that business transactions are prohibited, but i'm unsure whether this applies to any kinyan, or just where it was owned by someone. I also read that you cannot make something hefker on Shabbat, but nothing about taking something that's hefker.

This came up over a silly idea of making some chametz hefker, and taking possession of it on Shabbat, after Pesach has ended in Israel, and consequently being able to eat the chametz.

Answer 1

One may make a kinyan on hefker items on shabbos (R' Akiva Eiger 339:6 s.v. משום מקח וממכר, Aishel Avraham 371:7), provided that he does so in a way that is not evident to people that he's trying to make a kinyan (Shmiras Shabbos Kihilchoso 29:32).