If a bounty expires but the "best" answer hasn't been chosen, I know that half of the bounty is automatically awarded. Is it possible to then select one of the answers and award the other half? If not, what becomes of the unawarded points?
I don't see an explicit reference to this anywhere, but am almost positive that once it's awarded automatically nothing further can be done. Tell you what: A bounty I set is due to expire in about eight hours, without (AFAICT now) being manually awarded. If indeed it's automatically awarded, I can see thereafter whether I can award the rest manually.
Update: I checked now (some three hours after the auto-awarding of half the bounty) and I cannot award the balance of the bounty to either answer.