All about drag when a projectile comes back through the sound barrier and passes through its own shock wave in a way. More a problem for long range target shooters. A 7.62mm. military bullet comes back through the sound barrier somewhere around the 900 to 1,000 yard mark and gets very upset and unstable before it settles down again. I've put them all in the black at 900 yards and then had a job finding the target when dropping back to 1,000. Shotgun patterns are 3 dimentional and as Pooch says, each pellet will be a slightly different shape and even travelling at a slightly different speed even after a few yards so it is very difficult to predict mathematically. Interesting question none the less. Lagopus.....
