Because you're working with an F2 hybrid, it all gets more complicated.
You can get results slightly higher than a guess by assuming that the lightest chicks are female and the darkest male. These tells will no longer be visible when true feathers start coming in.
Female
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Male
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Boys may have a white or lighter "cap" at the shoulder.
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Girls tails often come in earlier and more precise. Boys tails can look messy and downy for the first few days. For most chicks, this is a few days to a week out.
In my experience (admittedly limited) boys seldom have head dots. Some breeds can be accurately sexed by the head dots alone.
This is the same boy as above. His sisters both had head dots.
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These are not absolutes. By studying these signs and others I was able to sex most of my cross-breed chicks by about two weeks, but I have been wrong (I was off on two of the last batch of 7, but one was a black chick). I am still learning.