Gemara

(Mishnah): Diceplayers may not judge or testify.

R. Yehudah: This is if they have no other profession. If they have another profession, they are Kesherim.

(Rami bar Chama): They are Pasul because betting is Asmachta (the loser did not resolve to pay if he loses, for he expected to win). It is not a Kinyan (the winner is not entitled to the money).

(Rav Sheshes): This is not Asmachta. Rather, it is because they do not contribute to society.

26b (R. Avahu): The Halachah follows R. Yehudah.

Shabbos 31a: Reuven bet Shimon 400 Zuz that he can anger Hillel. He failed, and complained to Hillel 'through you I lost 400 Zuz!'

Hillel: It is better that you lose 400 Zuz and (do not gain) 400 Zuz, than that I should get angry!

148b (Mishnah): (On Shabbos) one may make a lottery (to determine who gets which portion) with his sons and family at the table, as long as he does not intend to make some portions bigger than others. We may make a lottery for Kodshim, but not for the portions (this will be explained).

149a - Inference: One may not make a lottery with strangers.

(Shmuel): If a group of people lend to each other and are insistent to get back no less than they gave, they transgress (on Shabbos and Yom Tov) measuring, weighing and counting, lending and repaying on Yom Tov, and according to Hillel, also Ribis (usury).

Question: If so, it should be forbidden even with one's family!

Answer: Rav taught that one may lend to his family and take Ribis, to give them a taste of Ribis.

Question: If so, it should be permitted to intend to make some portions bigger than others!

Answer: Indeed, it is. The Mishnah is abbreviated, it means as follows. One may make a lottery with his family, even if some portions are bigger than others, like Rav taught. It is forbidden with others, like Shmuel taught. It is forbidden even during the week, for it is like diceplaying.

(Mishnah): We may make a lottery (for Kodshim, but not for portions).

(R. Yakov brah d'Bas Yakov): This forbids a lottery on Yom Tov to divide portions from a weekday Korban.

Rishonim

Rif and Rosh (Shabbos 63b and 23:3): One may not make a lottery with strangers (on Shabbos) less they transgress measuring, weighing and counting, lending and repaying on Yom Tov, and according to Hillel, also Ribis.

Ba'al ha'Ma'or: It is permitted with one's family, just like Rav taught that one may lend to his family and take Ribis, to give them a taste of Ribis. This shows that Hakpadah (insistence to get the proper amount) within a family is not called Hakpadah, so we are not concerned if they measure. We rule unlike Rav regarding Ribis, but regarding lots, we permit even if some portions are bigger than others. The Rif did not explain this enough.

Rambam (Hilchos Shabbos 23:17): One may not make a lottery or play with dice on Shabbos, for this is like business. One may cast lots with his family to determine who will get the bigger portion if some are bigger than others, even with one's family, even during the week, for they are not particular.

Rambam (Hilchos Yom Tov 4:20): One may not cast lots on portions on Yom Tov.

Rebuttal (Ra'avad): The Gemara forbids lots on Yom Tov to divide Kodshim of Chol. With one's family one may even divide big portions against small portions.

Rambam (Hilchos Gezeilah 6:10): If one plays with dice and stipulates that the winner will receive such an amount, this is Gezel mid'Rabanan. Even though the owner lets him take, since he takes it for nothing through frivolity, this is Gezel.

Question (Magid Mishneh): The Gemara connotes that the Halachah follows Rav Sheshes, that since he gives willingly it is not Asmachta. He is Pasul if he has no other profession, because he does not contribute to society. What is the source that it is Gezel mid'Rabanan? The Rambam himself disqualified only when he has no other profession! Shabbos 149b supports the Rambam.

Kesef Mishneh (Hilchos Edus 10:4): Since R. Avahu needed to rule like R. Yehudah, this shows that Chachamim disagree, i.e. they hold like Rami bar Chama. The Mishnah disqualifies a diceplayer if he plays with Yisre'elim for money, or even if he plays for free or with Nochrim, if he has no other profession. Perhaps Rami bar Chama meant to say this, but Rav Sheshes interrupted. It is possible that Chachamim agree, but since this is not obvious, R. Avahu needed to rule like R. Yehudah.

Hagahos Ashri (Shabbos 2:19): If people wagered, they acquired. This is not Asmachta. This is only through Kinyan Sudar. If not, they can retract.

Poskim

Shulchan Aruch (OC 322:6): One may cast lots to divide equal portions among one's family, to avoid envy.

Mishnah Berurah (19): Diceplaying applies only if one can profit.

Shulchan Aruch (ibid): It is forbidden with others. Since they are Makpid, they will come to measure or weigh. One may not cast lots to divide unequal portions even with one's family, even during the week, for it is like diceplaying. Some permit with one's family, for they are not Makpid.

Beis Yosef (DH umi'Pashta): The simple reading of the Gemara permits lots to divide portions of different sizes to one's family. The Rambam rules like this in Hilchos Shabbos. The Rif and Rosh brought only the Isur with strangers. Perhaps we may infer a Heter with one's family, for they are not particular. Diceplaying does not apply, for it all belongs to the Ba'al ha'Bayis. The Ran says that the Rif permits different size portions with one's family, and forbids even identical portions with strangers. The Tur holds that the Rosh would have said so if he held that the Rif meant this. Rather, the Rif forbids different size portions even with one's family. Since the Halachah does not follow Rav regarding Ribis, the same applies to portions of different sizes. The Magid Mishneh says that we rule unlike Rav only regarding Ribis, lest they continue the habit, but we did not forbid within the family (trading portions due to) diceplaying, which is forbidden only mid'Rabanan. We rejected Rav only lest they continue to do so, but letter of the law it is permitted. Therefore, it is a good proof to permit here.

Taz (4): If we are more lenient about trading portions because diceplaying is only mid'Rabanan, why did the Gemara ask why we may trade (similar) portions within the family? Also measuring is only mid'Rabanan! I say that we do not distinguish mid'Oraisa from mid'Rabanan. The Rambam's text holds that Rav permits to borrow on Ribis from one's sons, so they will enjoy it and save money to lend to Nochrim. He intends to accustom them to Ribis, so we decree lest they lend to Yisre'elim. We need not decree about trading portions.

Magen Avraham (7): Stam, we assume that his family are not Makpid. If they insist on a lottery, this shows that they are Makpid! When they are Makpid, one may divide unequal portions even without a lottery, lest they come to mention the amount of the measure.

Magen Avraham (8): Shiltei ha'Giborim (63b:3) asks that the Tur (207) rules that diceplaying is not Gezel! In Siman 34 and 370, the Tur says that it entails some Gezel.

Magen Avraham (9): We may not cast lots to divide Kodshim of Chol on Yom Tov. If so, there is no Heter even for a Mitzvah, if it was possible from Erev Yom Tov. We never permit on Shabbos, for there was Lechem ha'Panim (and we did not permit for it). However, the Magid Mishneh says that the Rambam permits.

Mishnah Berurah (22): Even though the Ba'al ha'Bayis owns everything and Gezel does not apply, we are concerned lest they get accustomed to play dice with others. All the more so it is forbidden on Shabbos, for it is like business.

Mishnah Berurah (24): One may not cast lots to divide onjects. We may cast lots to decide who wil say Kaddish or get an Aliyah. Many Poskim hold that there were lots on Yom Kipur to decide who will do Avodos. We permit lots from a Sefer, but not to pick cards from a bag.

Kaf ha'Chayim (31): We must be stringent about an argument of Chachamim, certainly for an Isur Shabbos.

Rema (CM 203:10): If Reuven and Shimon agreed to switch all they own with the other, Kinyan does not help for this. Some say that it helps.

SMA (6): The Rivash (263) says that it does not work. The Terumas ha'Deshen (311) says that it works. He agrees that it is Asmachta; Kinyan helps in an esteemed Beis Din.

Gra (207:40): The Rema says that wen people bet and do a Kinyan and it is not in their control, it is binding. He learns from Shabbos 31a.