It is a springer, using the "Giss" double piston system to achieve recoilless operation - state of the art competition rifle in its time and quite capable of good scores in the right hands even now.
A bit of info here;
http://bobsairguns.com/index.php?opt...lery&Itemid=53
and here;
http://www.airgunbbs.com/showthread....piston-systems
ATB
Mike.