A 12 hour gun safe? Did you mean 1/2 hour? Never seen one rated that high before, especially a gun safe.

Anyway, if the safe was sitting in the middle of burning coals for 5 days, I don't think there's much you can do to save it. A safe can only insulate for so long, but eventually the contents are going to heat up to the same temperature as the surroundings. A true fire safe might have worked a little better, but still that's a long time for any safe.