I need to see many more and better photos of the handful of twisted and/or melted things they found. When something departs in some minor way from contemporary objects of the same type (firearms in this case) it is likely the thing is a firearm. Many departures make it more suspect. I've never seen a m/l small arm of that era:
-with a conical barrel
-with a supercaliber chamber
-with a hook that thin
-with a hook that was a separate piece unless it was welded secuely to the barrel
-with two holes on top
-with a raised rectanguar platform like that one on top
What I'm trying to say is that firearms were new and mysterious back then, people did not know exactly how they worked so tended to make very slight changes from what worked before, when redesigning one of them. So to suddenly find a handful of separate parts, throw them together in a way they don't fit very well, and say "here's a radical historic gonne with five or more features we've never seen before" is a bit of a stretch for me.
Here's a link to a drawing of the famous Tannenberg Gun for comparison, note the long subcaliber chamber.
http://media.photobucket.com/image/tannenberg%20gun/Incitatus/TannenPlan690.jpg