ok, so you have removed the barrel from the receiver and looked on the underside of the barrel, the flat part, that touchs the receiver, there are no marks ?
you will usually see a proof test mark of some sorts.
if you can, snap a digital picture and post here so we can check this most cool little gun out.
i find this kind of stuff one of the most interesting parts of the hobby. that is, trying to figure out the history behind a firearm !
sg