Well Ron I set the Chrony [I have one of the original F version] up and tried a few loads. Blackhorn is a surprising powder I do not know exactly where the limit should be I do know that 140 grains gives just slightly more pressure than 120 grains of 777 and my chrony averages 3 shots at slightly over 2400 FPS with a 200 grain 50 /40 and they have shot accurately for me before I do not set up targets when I chronograph.
The 250 came out at 2240 FPS. Since my chrony is very old I am hoping I can get someone with a newer chronograph to check my figures.