Guns created by 3D printers "could be the next generation of firearms" in the UK, Greater Manchester Police said.
Detective Inspector Chris Mossop said: "These could be the next generation of firearms and a lot more work needs to be done to understand the technology and the scale of the problem.
"If what we have seized today can, as we suspect, be used to make a genuine firearm then today will be an important milestone in the fight against this next generation of homemade weapons.
"I would strongly urge anyone who has information about the whereabouts of a gun in their community to call us."
More top news
Northern Ireland's Health Minister Jim Wells has quit after sparking controversy over comments about gay marriage.
Prince Harry may not be able to meet his new niece or nephew until mid-May unless the royal baby puts in a speedy appearance.
A British climber trapped on Mount Everest after the earthquake in Nepal has said rescuers face "a race against time" to reach his group