I get 640 fps with AA field 8.44 grain, but only 620 with 7.0 grain gecos.
I think about 5 fps spread with both pellets
Just did my 2 with RWS R10 7 grain: 300SU average over 5 shots 643 fps. 300S 633 over 5 shots.
John
Law of any kind only affects those willing to abide by it.