I just had a closer look & now you come to mention it the rifle has a textured brunofixed finish which would be correct for a late war 4T but not for a L42. Also, there's no designation engraving on the body side wall. Looks like a real 4T action though. Flight RN, was it definitely marked up as a L42A1? Was the forend cut short........just wondered if it might have been a 4T that got mis-labelled as a L42.........?
Odd, but presumably it has some sort of provenance to have got into the GermanArmy Technical Museum.