I just made some reduced 221 Fireball loads this weekend. My gun has a 14 twist, and I chose to use 55gr fb sp's . I shot a few this spring with a similar bullet, so I knew about what to expect. I started at 5.4grs of blue dot, and ran it up to just 7.0 grs. This was worked up 2/10 ths at a time. The 5.4 gr load wouldn't stabilze the 55's , but 5.6 did. 5.8grs shot well, but I settled on 6.8grs with a .270 group at 50-55 yds.
I didn't even play with seating tests as I don't have many of the bullets on hand. Hopefully I get to shot thru a chrony to see where I am, but I suspect I'm around 22 mag speeds or a fuzz more with a 55. A 12 twist would of allowed me to go lower than 5.4grs if I wanted, but I'm about where I want to be.
Update: Shot two of these 221 loads loaded at 6.8 gr across a chrony yesterday. 1st went 1829fps and the second seated 0.0015 deeper went 1860 fps.