Just a couple of points, all pretty well non contentious. Early lesson during basic projectile properties was that the projectile doesn't care a fart about what's happed where it's BEEN. It's only concern is where it's going to pass because that is what is going to affect it. I wish I'd learned the exact phraseology as it made so much more sense. The next bit was that the barrel is nothing more (?) than a simple tuning fork. Not sure that I'd necessarily agree with that because it is a tad more complicated but that's how I learned it for exams! And how true BinO is when he repeats again and again the fact that the barrel don't only vibrate in one plane.......... It's vibrating in ALL planes and this is further complicated by the fact that while all the wood ain't the same, nor are the steel properties.
The only people who would REALLY and truly understand the greater technicalities of a barrel are music graduates because it's really all about vibration and harmonics. And while we're on about really truly great harmonics, sad day for the loss of Phil Everly. Want to hear some great harmonics, listen to a little known/played number. So Sad by Don and Phil Everly