Reread the thread, 22" barrel producing >3100 isn't bad. Not sure why a small primer would reduce velocity beyond what another .1gr of powder would accomplish. Probably will have to bush the firing pin if it's stock pin to get a lot more velocity with a small primer.
My 6.5x47 Lapua w/small primer slings 140 bergers at velocities that would embarrass most 260s.