I wonder if it is a matter of hardness or of adequate shotcups and buffers? IF I understand correctly, buffers are used with HeviShot to reduce bridging of the hard pellets, thereby reducing damage to shotcups and, when shotcups are breached, to forcing cones.
For at least a few seasons, I have enough bismuth and Kent TM loads to see me through. Maybe by then this murky world of non-"steel", non-bismuth, non-Kent TM, nontoxic shot will have become more understood. Perhaps then those without adequate stocks of bismuth and Kent TM will be able to purchase with confidence for their old doubles.
Niklas