However, the shop owner, speaking on condition of anonymity, said the supposed trigger and magazine for bullets were actually parts of the printer - which he uses to make models.
In tears, he said: "I'm angry, disappointed and hurt. This could kill me, this could threaten the business. I was sat here yesterday morning and I saw police officers coming to the door. I just thought it was a customer. We have officers who are customers.
"They came in and said 'We have got a warrant to search this premises'. They accused me of making gun parts."
Presented with the "trigger" and "magazine", he explained that one was a spool and the other another part of the printer, to which he said the officer replied: "Oh! OK." "Andrew" was released an hour later on bail.
US-based plastic gun maker Cody Wilson said 3D printed guns will be part of Britain's future, in an interview with Sky News.
Mr Wilson, who is the founder of a company that publishes gun designs online, said Britain's attitude towards firearms was "schizophrenic".
I'm really excited about, what I call, the digital apocalypse.
I think countries like the UK...where your culture is schizophrenic, scared of itself, post-heroic and is unwilling to deal with the idea that people will have guns again - somehow like it's a feature of Britishness.
I think that's absurd and I can show you that's disappearing.
I'm saying that your future will have these as a feature irrevocably from now to eternity and this is something that's bleeding into the present.
The discovery of a plastic magazine, trigger and the 3D printer used to create them during a search in Bagley, Manchester, was hailed as "really significant" by Greater Manchester Police.
This is a really significant discovery for Greater Manchester Police.
If what we have seized is proven to be viable components capable of constructing a genuine firearm, then it demonstrates that organised crime groups are acquiring technology that can be bought on the high street to produce the next generation of weapons.
In theory, the technology essentially allows offenders to produce their own guns in the privacy of their own home, which they can then supply to the criminal gangs who are causing such misery in our communities.
Because they are also plastic and can avoid X-ray detection, it makes them easy to conceal and smuggle.