Got it. Thanks.
Can you calculate the resonance or is it trial and error?
From my experience it's trial and error, but not too hard to work out. Depending on the caliber (I shoot 6ppc) you try three shot groups starting at a low powder charge and increase between .3 and .5 grains with each charge. It doesn't take long to find the best "node". Usually there will be a couple of them. After you have the correct powder charge you start working on load length...how far the bullet is seated in the case.
All of this assumes you start with an appropriate bullet for the barrel twist. I shoot a 13.5 twist barrel (i.e. one revolution in 13.5 inches) and select bullets ranging from 62 to 68 grains. Bullet shape makes a difference as well. Sometimes a particular bullet won't shoot well in a barrel, but another with a different shape will.
Obviously I'm handloading and I use bullets from custom bullet makers so I have a wide variety of choices.
In benchrest we load at the range so we can tune the charge during the match. If my load is not working I can increase or decrease the powder charge for the next group.