Not to spoil anyone's fun by reverting to the subject, but... the calculations of the effect of a swinging barrel on the horizontal axis of the (non plastic cup-wadded)shot string whilst being interesting in themselves, can be tested against experiment.

I've tried to produce the effect by rapidly swinging a gun (felt wads)and shooting at a pattern plate ... nothing.

I suspect this is for two reasons; the effect if any is very small, and at the moment of ignition the recoil stops most of the swinging motion anyway. In any case try as I might I never saw any much difference in the patterns thrown by a swinging barrel as against a still one.

You can get a rough idea of the comparative length of a shot string by listening to it hit the pattern board.

Eug

Thank you, very kind. Mine's a pint