How do I make it so there is no turn limit in single player? I want to keep going until everyone is dead

Using the Custom game option in single player, you can set the # of turns
up to 50. There is no unlimited turns option. On some occasions, it may
become impossible to reach or kill a target no matter how many shots, due
to low power, distance, location, or defences. In this case, the bots usually
Skip, resign, or declare a stalemate.