I am using 24.5gr of Accurate 5744 under a 425 Lead/FNGC for low 1,200's from an 18.5" GuideGun.
5744 is
extremely consistant even w/ low case fill. I recommend it w/o hesitation.
Accurate's website says 21.0-21.5gr under a 500 grainer will do what you want.
See:
http://www.accuratepowder.com/wp-con...d_data_3.5.pdf