I see little to no point in taking a 10 bore with no choke and degrading any performance the ammo may yield by dropping the pressures (and resultant velocity) and attempting to down ducks. If you want to go fowling, use ammo which is intended for the gun's whole barrel, not 4" of it. Modern wads are dimensioned to fit a barrel diameter, and seal the gasses to achieve some sense of killing power. Wounding game for the sake of using a particular gun isn't responsible, in my estimation.
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