2-p, I most surely wish I coulod find the article on the Remington tests (it was in a "major" publication). I was well enough scooled and experienced to be critical of their test equipment and method and found no fault.
Small problem with the "velocity check" idea. That is that even a small barrel obstruction will sometimes cause a gas hammer capable of bulging the tube. I'd have to hypothesize that any "velocity check" would do likewise.
Seems to me that each individual piece of shot will accelerate forward at increasing velocity (and lower shot swarm internal pressure) just as each gas/liquid atom/molecule does in true fluid flow. The counter intuitivity of the venturi principle is one of the reasons flight came about at least half a century later than science might have supported.
The report of systematically lower recoil from higher MV makes me suspect there was some test error. As I recall, the Remington test measured MV over only a few feet. 20 yd is a "fur piece" and could have introduced some measurement error, IMO.
Further, IMO, the reduced internal pressure of the shot swarm is the reason the pellets stay closer together. That is, they have less pellet-to-pellet pressure and less force to cause "spring-apart" and the entrapped air has less pressure to cause sideways velocity as the air expands on muzzle exit.
DDA
