"Are patterns from a shotgun barrel affected by harmonics? Will my shotgun throw a more dense and more even pattern if there is some way to control the harmonics of my barrel?"
Several years ago, I searched for information on the effect of harmonics on shotgun barrels and could find nothing on the subject. That inspired me to begin a years-long research project that provided answers to some of my questions.
Recently, I was in a conversation with a man who is outstanding in the field of medicine and who also, when time allows, is a shooter. When I mentioned the study that I had done on the effect of harmonics on shotgun barrels, he paused for a few seconds and then said, "That is the nerdiest subject I can imagine."
I really could not disagree with that statement. However, having spent several decades evaluating various shotgun patterns and counting many more holes in 10" circles than I care to recall, I believe that there are a good many "shotgun nerds" out there.
So, for those of you who may have missed the article the first time around or might just enjoy reading it again, here's a link to that article: https://allaboutshooting.com/blogs/blog/98758599-harmonics-in-shotgun-barrels