The HIKS R40 is a prototype weapon that can be found in files of SAS: Zombie Assault 4. The HIKS R40 and its / versions are mentioned in a CSV file located in the game file of SAS 4's mobile version. Further, a picture of its normal version exists in the game file, and, on top of that, the top-down image of it (which would be seen when the player holds it during gameplay) is in the file.
The R40 is most likely an earlier model of the HIKS M1000 in the game's development, as it is nearly identical to the M1000. The only differences between these guns is that the M1000 has a large drum magazine while the R40 has a box magazine and the M1000 has lots of small barrels while the R40 has one large one. It was also included in a "practical joke" by spool where he showed a picture of the R40 with the stats of the M1000.
In the official trailer for SAS 4, the Heavy class character is shown holding the R40. Later in the public (and current) release of SAS 4, the Heavy's image was changed to it holding a weapon that resembles the HVM 008. The Medic and Assault character's weapons, the CM Gigavolt and RIA 20 Striker respectively, were kept the same.
In SAS 4 beta, the Heavy SAS's picture shows him holding the R40, making it likely that the R40 is a LMG.
This is a prototype weapon which was a placeholder for another weapon which is going to be removed from the game files someday (Not right now as of March 23, 2016) confirmed by Spool.
The Heavy holding a R40 in the trailer
HIKS R40 mentioned in PC's swf file
The HIKS R40 mentioned in a CSV file in the mobile version's game file
Top-down view of the R40 from the mobile version's file
Spool saying that HIKS R40 will never be a weapon and it's a prototype.