An unusual experience with shot concentration happened to me on a dove field some years ago. I was shooting a .410 O/U and was closing in on a limit. Here's the copied and pasted description from a thread I started 8 years ago about the event.
"I was shooting a new to me Verona 30" O/U .410 with two fixed full choke barrels. I had previously patterned the gun with 2 1/2" loads to look at the point of impact of both barrels, as it seemed to be stocked a bit high for me. The patterns at 30 yards were what I expected for full chokes, and regulation was good. So, I bought a few boxes of Remington 3" loads, 7 1/2s at 1135 fps and took it to the dove field that Saturday afternoon. I was working towards my limit of 15 pretty well when a dove came from right to left, almost a 90 degree crosser, well within my range. I swung and shot, and immediately noticed a small object in the air off to the right side of the dove, and watched as they both hit the ground. Wondering what it was, I never took my eyes off it until I reached the bird. To my amazement I was looking at the dove's head laying on the ground some 5 ft. from it's obviously lifeless decapitated body. Upon closer examination, the dove's body was not excessively shot up, nor it's head. They were just completely separated from each other. I went back to my stool, sat down and began to wonder what had just occurred. I got back up and stepped off the distance from my stand to the spot it fell, calculating a distance from gun to bird in the air of 23 yards. Understand, I clearly saw the dove's head leave it's body upon impact of the payload."
For the rest of the discussion, and "sleuthing" by many contributors, read here:
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=377979&page=1
