Interesting article.  I'm not currently set up to load shotgun ammo but I would definitely try some subsonic stuff.   

Agreed but I'm a** deep in things that need doing right now.  Loading my own ammunition is going to happen again at some point but right now my stuff is all in storage.  When it gets set up again I will be adding a shot shell set up to the existing equipment and then it will be time to play around with subsonic loads - unless I can find some factory made stuff in the interim. 

I'm thinking you might also be able to make some fairly uncomplicated subsonic loads using either Trail Boss or even Blackhorn 209.   

I was thinking of Trail Boss as a powder friendly to the dipper method of dispensing it and using it with cardboard and fiber type wads.  I understand that it does not like to be compressed as breaking the individual granules causes erratic pressure spikes.   Blackhorn 209 has worked pretty well in a buddy's inline igniton muzzle loader and he thought about trying some shotgun loads with it so I got interested in it for that use as well.   He also uses Trail Boss in some old straight walled cases like 38-55 and .32 Winchester Special so I've seen it in actual loads in actual rifles I have handled at the range.

Back during the great reloading component shortage he was able to find Blackhorn 209 and Trail Boss when there was little else on the shelves so he used what was available.      

And for the record I find your powder descriptions spot on.