Unless cutting down for a can I usually stop at an arbitrary 21" even with the medium sized cartridges. It seems to me a recessed target crown, what I call the floor mat crown, directs the noise away from the shooter better than the flatter crowns. You could take a hack saw to the barrel and try in in one inch increments until you got what you wanted and then have a gun smith cut it properly for you. Might leave an an extra quarter inch on for him to work with.

Noise is critical or the blast but balance is the first priority for me. I like a front action screw balance point with a slightly muzzle heavy feel. This just shoots better for me.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli