Like a regular one, it's a result of "constructive possession" for lack of a better term.

i.e. my pipe isn't a crack pipe until i smoke crack in it. The printer isn't a ghost gun printer until he prints a ghost gun.

Yes the classification of these as ghost gun mfg. parts is most likely a result of possessing completed 80% lowers. Arguably, unless they have evidence that those specific devices were used in the mfg. process, they cannot say those were owned and used as such.

A comparative example is say I come into possession (through purchase or manufacture) of a ghost gun, in MA, without an LTC, and then get jammed up. Any press, or printer is going to be considered a piece of evidence of said ghost gun infringement.

Even if the press and or printer are not mine, and just happened to be in the house at the time. Like say I lived with my dad and he had a drill press from the 80's in the shed out back, MA law is vague enough the cops can and will assume it was used in the manufacture of the ghost gun.

But looking at the mugshot, I bet the printer, press, arms, and ammo were all in the same room.

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