The Astra 680 was introduced in 1981. It's a variation of the model 250 with minor changes in the shape of the frame and recoil shield. This might just have been to make manufacture easier. Both my 680 INOX and my 680 AL have 6-shot cylinders, this is a definite improvement.
The 680 was available in blue, stainless (INOX) and with an alloy (aliminium?) frame (680 AL).