Everyone who has a bump stock has 90 days to turn them in or become a felon.

From Breitbart:

The Department of Justice is amending the regulations of the Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) to clarify that bump-stock-type devices-meaning “bump fire” stocks, slide-fire devices, and devices with certain similar characteristics-are “machineguns” as defined by the National Firearms Act of 1934 and the Gun Control Act of 1968 because such devices allow a shooter of a semiautomatic firearm to initiate a continuous firing cycle with a single pull of the trigger.