I recently found a round in a second-hand shop’s “odds and sods” bin hstped "SAKO/5,7

This is the metric name for the 222 remington

Thanks Pivi.
Any idea about extractor groove?
I will attempt to upload pic.

I don’t know why your sample has got a different extractor groove,however I have seen many 308 winchester cases ( for example) with different extractor groove heights.It could also be a case feature made only by Sako