Veteran .22 tuning

Any ideas how to tune “The Vet” .22 ? No changes, everything straight from the factory. No matter how I set regulator pressure, max speed is 850-860 with new 25.39 redesigned monsters. Max that I want is 920-930. I don’t want to grinding transfer port because ther’s no spare parts.. Maybe thicker hammer spring ? Maybe bigger regulated aera ? I don’t know.. Any ideas ?