Several tools available good ole fashioned fun and load workup. Some like std dev., and extreme spread, but I have kinda proven that wrong many times, but it does give you useful data if you plot it versus load. Ladder method you mentioned. Which by the way, can be useful, but needs to be repeated a few times at least, to get useful data and I find really only useful in a semi-premium gun at best. In other words, trying to do it on a dud, will produce dud results. A barrel is a dynamic beast to say the least, and when you add humidity, heat, fouling, it gets down right tough to interpret ladder method load workup. Definatly can be done, but many trips are warranted.

Lastly, good ole shoot and see if there is promise. If you see a load within a grain there is promise. Next start changing OAL by some differnet amounts. I have found changing COL can have a dramatic impact on accuracy, and this has been proven many times to be the effect of your harmonics nodes you mention.