Glad you had mostly a win mate - of sorts!
When you do go sub sonic it will be a muted bang, I can do that with my M92 in .32-20. 115gn cast pills & 2.5 gn of Trailboss - only gets 800fps. I thought I did a dud (primer only load) & that the bullet was still in the bore, only when I looked at the chronograpgh did I realise that it had exited the bore. Frightened the hell out of me there for a while!
As you go down in load watch the chronograph like a hawk, (don't get one stuck for God's sake) mine are pretty consistent; just on/over 800fps & as QL suggests about 53% capacity (usual warning applies to all loads stated anywhere)works in my little rifle OK & not too bad accuracy considering my eyes aren't the best anymore.
Good fun mate!
Cheers
93x64mm