Strangely enough, the early metal modelguns command a premium price [among models]...Here is a site where they can tell you what you have (if you take enough pics!) and what it's worth...
http://mp40modelguns.forumotion.net/
Those metal modelguns are illegal in some areas - Like New York City or Nassau County in NYS...
They are collectible...Re-enactors and stage prop people, as well as static display props...The better ones [MGC as alanint said] are much sought after...
Yours looks quite detailed...Some of the modelguns actually will chamber a fake cartridge which gives off smoke, noise, and sparks...Quite realistic...