This is the MT6400R1 which was an LE6940 that was converted to be ban state compliant. This variation is not seen on the market very often.
The MT6400R1 has a plain unthreaded barrel with no bayonet lug. It has a fixed carbine stock that is mounted on a buffer tube that goes to the end of the stock.
This example was seen for sale on http://www.ar15.com on 26 SEP 2019 for $1600.00