Help identifying Pelikan model

[Snowstorm]

Hello

I recently acquired this barrel, thinking it was a 400NN. When it arrived it's a bit smaller, and I can't seem to find a reference online

Length is about 3 7/8", colour is a tortoise with an iridescent to it, on a green translucent background. Section and piston know are dark brown and not black

400NN nib unit does not fit. It is threaded internally for a nib, but the 400NN unit is to too large to fit in. 400NN cap also does not fit.

Its next to a 400NN in the photos for comparison

Any advice appreciated on identifying this model.

Thanks in advance