I had mine cut to 18” and it just shouldered.....I also added an 0-ring adapter that was nearly a perfect match for the barrel profile and ensured a good shoulder for my can. I am out of town but will put up a picture of it next week.
i had mine threaded for a dead air can. he was actually supposed to cut the barrel down but didn't and i'm fine with it the way it is. triple river gunsmithing was recommended by cz so that's who i used. mine's a lefty also not that it matters.