Re post 854, a shot charge never acts as a solid.

From the moment of ignition, set back and deformation commence. The shot charge shortens under acceleration do to compression of the shotcup petals and the malleability of lead.

When the charge hits the chamber cone, it lengthens behaving more like a fluid than a solid.

It lengthens again at the choke, if there is one.

'Ballistic coefficient' is meaningless within the bore, and only relevant to individual projectiles once bore exit occurs.

"The price of good shotgunnery is constant practice" - Fred Kimble