24 inch
I know some smith's will always cut a barrel to 24" or close to it if possible from the blank. Their thinking is that they have a very close tune number that works at that length that they shouldn't be but just a few clicks of the tuner away if the barrel will shoot. I understand this logic completely and it may be mistakenly, but I try to get as much as I can out of any blank that I do and just work towards tune from there.
Tad