Extremely high speed photography showing photos of the shot charge at the muzzle might help explain this, but what happens before the ejecta leaves the barrel is only supposition. I kinda agree with wonko (for a change) on this.
He called a bs flag, fine, but only Stan provided sources to investigate.
It is a proven fact as far as I'm concerned, that a single lead bullets' nose will deform back towards the base on firing, and the nose will show deformation after it clears the muzzle even though it didn't touch some wad material, other shot or the barrel.
Wonko joked about Newton and science. If a hundred, or pick a number, shotcup pellets made the ride down a barrel unmolested. Why wouldn't the leading surface of a perfect sphere deform back to some degree of out of round. Then again, there's decent evidence that the individual pellets do get affected, by unevenly applied physics, on their ride down a bore.
If someone were willing to accept the high speed photo evidence of shot after it left the muzzle, and not willing to accept any setback concept, then it must be the choke? Why would we get deformed flyers out of a cylinder bore? Wouldn't it be fairly easy to confirm how true the pellets were before loading the test shells, and couldn't we take a couple apart to make sure our loading technique didn't damage the shot?
