Why is it the only one??

[aerelm]

The reason behind this probably is because weapons don't have an actual "Range" value assigned to them in the game files, so for someone looking at it under the hood, that difference in range wouldn't be as apparent. The actual values each gun gets that decide its range are projectile speed and projectile lifetime (i.e. how long the projectile lasts after firing), so the range of the gun is not listed anywhere in the files other than its infocard (which is purely visual, and in a whole separate file). FLEngine has lots of wonderful little quirks like that. I'm guessing the weapon was initially 750ms and was later changed to 700ms, but there was an oversight and they forgot to update its lifetime, hence the lower range compared to similar weapons.

Just post a bug report about it.