They were fairly high power (for the era) rifles, manufactured for quite a few years. Early ones had leather piston seals. I had 2 in the early 80s that were more powerful than my Fwb124 and as accurate but a bit clunkier ergonomics. RWS sold a good number so they should not be rare but I don't see them much. There were synthetic piston seal conversion kits available for a while for the leather seal versions . Not sure any more . Not the easiest to work on, either . If it's a 177 and healthy, it should shoot over 800 with 8 grain pellets.
Bob