This is apparently one of a prototype example that was made to experiment with different cartridges in the T-14.  It is well known that the 8mm Nambu round was under powered for combat use and it makes sense that the Japanese would try more powerful rounds.  This gun chambers a .30 caliber Luger round.  The barrel is obviously different with a more gradual taper from the receiver and the sight attachment is totally different than a standard T-14.  Interesting gun.