Bronko, you didn’t specify your swabbing method. Curious what you used. Spit patch? 50/50 Hoppes/alcohol?
Also, I can’t recall (I’d have to look back at my notes) ever getting great accuracy with BH209 with that light of a charge. I generally run 110-120 grV.
I’ve never tried BlackMZ, but the beauty of BH209 is you could shoot 15-20 or more shots in a row without swabbing and you’d still be shooting that same group. No way to do that with the other subs. And the only limitation there is your breech plug carbon build-up. If you keep your plug drilled out every 5-10 shots, you could probably shoot 100 shots into that same group.