gauge in pattern vs gauge in stockinette
I'm about to start on a vest in moss rib stitch, pattern from Silver Creek Classics. The pattern gives a gauge of 5 1/2 sts per inch in moss rib stitch.
When I measure my swatch, I get 7 sts/inch when the rib is relaxed (scrunched up), but only 4 1/2 sts when gently stretched out, or in stockinette.
My yarn is a light worsted, whereas the pattern says it calls for sport weight (but says 240 yards/4 oz, which is more like light worsted I think).
It doesn't make sense to me that with bigger yarn, I would get a gauge with MORE sts per inch than the pattern. Is it reliable that the gauge really does mean in the moss rib st, and not accidentally be in stockinette although it says it is in the moss rib?
I'm stressing out here (can you tell?) trying to figure out the right number of stitches to cast on.
Anybody have experience or suggestions? Many thanks.