This is an ac44 with a FN frame.  FN frames were made by Fabrique Nationale in Belgium under German occupation.  The frames were shipped to Walther and to Spreewerk.  Spreewerk examples are rare and appear in the early "x" block.  For some reason FN frames are not found on Mausers.  Walthers with a FN frame are somewhat uncommon but can be found in nice condition.