Auto. rifle upgr. internals is a weapon mod for the automatic rifle in the Fallout: New Vegas add-on Dead Money.
Increases the automatic rifle's rate of fire by 10%, thereby increasing shots per second from 6 to 6.6.
The vending machine code for the mod can be found in Puesta Del Sol South, directly behind the cables where you left Dean Domino during the Strike Up the Band quest.
After obtaining the code, the mod can be purchased from any Sierra Madre vending machine for 250 Sierra Madre chips.