Independent Journal Review (IJR) reports what the FBI has to say about Nevada requirement for background checks for private transfers of guns
Quote from IJR
In November, Nevada voters approved expanded background checks for private transfers of guns by requiring an FBI National Instant Criminal Background Check. Now, the FBI has told state officials it has no intention of fulfilling those requests because state law shouldn't dictate their manpower requirements.
California passed a referendum, Prop 63, requiring NICS background checks for ammo purchases. I interpret the Nevada example as an indication that the FBI will refuse to do background checks for ammo purchases.
Essentially if this turns out to be the case: FBI to Lt. Gov. Gavin Newsom: Pound Sand.
This also applies to Michael Bloomberg. FBI to Bloomy: Pound Sand.