Which checks yield an auto success on a 20 and an auto failure on a 1? The text confirms this for thief proficiencies and attack rolls. The text says a 1 in an automatic failure on a break door check, but that seems to be about it.
What about saving throws? What about proficiencies in general?
Not 100% sure about saves and proficiencies RAW but a 1 is always an auto fail on a save in my games from BECMI-3rd ed and clones and 20 is always a success with the exception of skill checks in 3rd ed if it has an uber high DC.
There’s no answer in the rules-as-written, unfortunately. In actual play, I have always ruled that for anything labeled a “throw”, a natural 1 is an automatic failure and a natural 20 is an automatic success. This would include saving throws, proficiency throws, attack throws, etc.
If there is ever an ACKS 2nd edition I will make this explicit.