Per http://www.bandpusa.com/files/db_trio.pdf
the F2 Classics run almost 10,000 PSI. Wouldn't use them in a Flues but they are my pheasant load in my Sterly also.
I'd stick with one of these:
Polywad 'Vintager' http://www.polywad-shotgun-shells.com 800-998-0669
Eley subsonic/low recoil http://eleyshotshells.com 512-821-9953
ARMUSA 'Vintage' http://www.armusa-performance.com 281-381-7773