The builder calls it an
MG47BP. Need to register to see the pictures, but there's some higher-res versions of the one you have
here.
That gun seems to be about the only belt-fed bullpup, which reminded me of another probably-unique configuration:
an open bolt revolving shotgun (I guess?)
TSKIB SOO made a revolving shotgun, which I think is really good looking:
Then they made a tactical version, which isn't.
Then they made a pistol version, because they're just the very best kind of crazy:
