A3-21 Plasma Rifle is special it comes from the missing android quest, I know a trick to get both rewards with no consequences.

After u find Pinkerton and get contacted by the railroad you can tell Harkness the code to revert him to an android. You can tell him and he will give you his rifle, don't chose the option to kill them. Go to Zimmerman in the lab tell him that Harkness is the android and you can get both rewards. also for those who delve into back stories Zimmerman is also an android.