Don't know about GARRETT loads but from info from "supreme loads for the 45/70" book show top velocities with(in order): H-335,AA2015,H-322, some of the loads eclipse anything that Garrett makes/sells. Reloder #7 is another good powder for top end loads. I will not quote any of the loads here as it draws alot of scorn from those entrenched in current commercialized 45/70 load doctrine.