Let's analyse that for a second.
We'd have to start by ignoring the fact that they couldn't find a statutorily valid way to call these a machine gun for over a decade of trying. The statute's language simply can't define one as a machine gun.
So skipping that and just saying a bump stock IS a machine gun, then you would need to do an analysis on whether a deactivated bump stock was "readily convertible" into a bump stock. - Like any collapsible stock is if you hold the detente open, and mount the pistol grip to the stock.
This whole thing is untenable from the perspective of ap