They seem to have no right click option. What do you do with them ?

You collect enough parts of the same weapon and then create one of the new guns like the FAMAS. I believe its 4 unknown parts (the same type though) to create one of the new guns.

are you sure? you can craft the guns yourself if you have enough "unknown gun parts" of the same type?

i thought igor the gunsmith is the only way to get this guns...

...like miggs showed in his video:

Indeed you are correct Andex my friend. I have lots of the parts now, I just havent tried the next part to get one created - I was hazarding a guess. Perhaps Ill try later tonight but Im still looking for my Mod 48 and G17 Had no luck now for over a week.

I seen to get the L110 and another which I cant think of right now - but Im getting them over and over again at Martins barracks