This modification decreases the spread of the holorifle by 0.25 from 0.4 to 0.15.
The vending code for this mod is found in Puesta del Sol south on top of the tallest roof. To get there, go into the ruined cafe and exit through the top floor (exit located southern part of cafe, not north or east). Follow the rooftops to the center building in the square and you will see grating leading to the platform above. The vending code is on the ground at the base of the center column opposite the ramp you came up, near several microfusion cells.
It is stated once you enter the Villa that Elijah created the holorifle himself, but despite this the mod box is labeled with "Gun Runners". This is explained by the fact that it is the default appearance for a mod if it does not have its own GECK render.