The Gemara in Bava Batra page 106 brings this idea that brothers that inherited property, since if they cast lots, then the lot determines who receives what. It is hard to know what kind of "kinyan" [method of acquiring] a "goral" [drawing lots is].

In fact, the Tur brings [from his father the Rosh] openly [Hoshen Mishpat 177] that drawing lots in fact causes not acquisition to occur. It only verifies which part of a property goes to whom.

Yet at the same time he also bring down that Gemara from Bava Batra.

Rav Shach explains  that there is a debate here between the Rosh and the Rambam. With the Rambam there is a difference between a courtyard that is 4*8 amot [yards] where there is a law that either of two partners can force the other to divide; and one that is smaller in which case the goral [lot. i.e. dividing by lots] does not cause a acquisition. In the large courtyard since it is large and one can force the other to divide, then it is as if he already owns his part and the goral can verify which part.

To the Rosh there is a difference between inheritance where the inheritors never made a partnership in the first place, and in that case the goral can verify what part goes to whom, and in a sense causes the acquisition. [That is the acquisition is already there, but the goral verifies to whom is what.] 

But, in the case of partners, since they made an act of joining together and a goral can not cause a acquisition, there it only verifies.