No. Spreading or stringing from gun motion has never been observed.

A crosswind, however, would drift the slower and later to arrive pellets more since they are subjected to the wind for longer. Of course if your right angle target is flying downwind, this will actually reduce the shotstring length...

Yes, I know it ain't much but it could probably be measured by a dedicated experimenter.

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