When you ask for the value of this airgun, you need to give me more information than "How much is it worth?" Let me explain. If I asked you "How much is my 56 T-bird worth?" The first thing you might ask is, "What condition is it in?" It could be a real gem or just a bucket of rust. It's the same with any antique. The current condition determines the value.
You need to give a description of the airgun, give it some sort of rating like, it's in (Poor, Fair, Good, Very Good or Excellent) shape. Or tell me that is looks well used or has very little wear. Something that gives me an idea of where to start. Without more information it is not possible to give you an estimate of value.
BTW your air rifle was made between 1927-1939
Torbjrn Tnnsj has written: 'Du skall understundom drpa!'