Please expand on “resonance”. I’ve never heard of it and want to know more.
Gun barrels vibrate as the bullet travels toward the muzzle. You can tune the load by increasing or decreasing the powder charge. Think of the barrel vibration as a sine wave...the goal is to have the bullet always leave the muzzle at the same point in the sine wave. It needs to be either at the top or the bottom.
I shoot benchrest and in that game the difference between a gun being in tune or out of tune can change group size at 100 yards from (for example) .150 to .300. The gun has to agg under .200 in good conditions to win, so it makes a big difference.