Loaded up 20 supersonic and 20 subsonic today with some 2400. It's the only powder besides VVN110 that I have that is suitable. All velocities are the average of 5 shots.
220 Sierra Pro-hunters @ 2.26"
9.5 grains:
1006 fps
10.0 grains:
1060 fps
240 Sierra Matchking @ 2.265"
9.0 grains:
1044 fps
175 Sierra Matchking @ 2.255"
9.8 grains:
1087 fps
I'll try the 1680 next week, but I really don't think that is going to solve the problem. I think it's something else, but don't know what. Any other suggestions? I'm thinking about single loading some 240's out to the lands to eliminate the possibility that it is the extremely long throat of the Blackout chamber. Sound reasonable?