Same ammunition from Norma, Tikka TAC A1 (24" factory barrel) rifle, I fired 40 shots and measured 2611.5 fps average velocity and 15.41 fps SD.
5 shots still seem too few to have a conclusion as close as possible to the truth, and always with a small number of shots I had a lower SD than the real one. That's why when I want to have a real conclusion I use somewhere around 20 sample size shots