If the day was a constant overcast (obviously not dark dark though) with conditions constant that is what my old F1 used to like. The bright sunny days gave it hell, even with diffuser screens attached. One outing CED was telling me every second 22RF shot was doing 3300 fps and a mate shooting at the same time with an Oehler 35P was missing shots. Just the issues with an optical chronograph.
If you have genuinely lost 170 fps you should see that at the target with a change in group centre but you said your elevation was only a bit low. A drop in velocity of 170 fps when shooting to 1000 meters is roughly 1.8 meter shift in elevation but I guess you have already worked that out.
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