No you're right, the only part of a gun that qualifies as a gun is the frame or reciever piece, probably whatever houses the trigger and magazine. I found this out back when I was shopping for 1911s, I looked at the parts list on Kahr Arms/Auto Ordnance and found a disclaimer on the frames for sale that said you needed an FFL cause it qualified as a firearm itself. Other parts are just hunks of metal. I bought a hammer strut, the pin, magazines and grips at a gun show no problems and I'm 17.

That's true. Only the frame is the 'firearm'. But all our blank firing pistols have the frame, so they're firearms. We can swap out barrels and slides (which are unregulated .... SO FAR...) all day long. I'm not sure if there is any sort of remaining controversy on this thread ;) So I will amble along......

I saw an FG42 in the background in the movie The Eagle Has Landed, duribng the trainyard standoff. However, it might have been a rubber prop or something, it isn't seen for long. Also, I saw 2 StG44s for sale at a gun show recently.