Hypothesis
The Fiocchi ‘Pigeon 32’ cartridges that I have been using appear to cause excessive wounding.
Earlier investigatory testing on the pattern plate (at various ranges with various chokes) showed these cartridges behaved erratically; the pellets tended to stick together with a lot less pellets than expected hitting the target.
Better shooting performance could be achieved by trying two readily available brands and undertaking pattern testing in the method described by John