Everyone has their stories about gauge swatches. This is mine.
(Assume that the Law and Order scene change noise is inserted here.)
I don't swatch for socks anymore. I've knit oodles of socks, and the majority of those socks have been with a fingering weight yarn. I can order yarn and just knit it right up, no issues, and have it fit. I cast on 60 stitches, always, with fingering weight yarns.
I have some lovely Sockina Cotton, which is nice and soft cotton with a little nylon and stretch to it. Ravelry claims it's fingering weight. I cast on 60 stitches. Knit half a dozen rows in ribbing. And proceeded to put two feet into the opening. I should've taken a picture!
I then cast on 54. Knit half a dozen rows. Still too big.
48 ended up being the magic number. There's no way this yarn is "fingering weight"!