Haroon Iqbal, 32, from Birmingham was identified by police in the UK after an operation by US Homeland Security agents saw the seller arrested.
Gun parts as well as the 3D printer and an ammunition press were recovered from Iqbal's business address.
Head mitted attempting to possess a firearm and was jailed for 27 months.
The National Crime Agency (NCA) said using a different identity Iqbal had placed an order for the internal parts of a Glock 17 from an online seller in January,and asked for it to be disguised under electronics.
That was intercepted on its arrival in the UK on 22 January and the gun parts were forensically marked so they could later be identified.
However, the NCA said after the US based supplier was arrested, undercover officers in the country posed as the seller in discussions about a second package.
In that order, Iqbal requested a Glock 17 barrel and automatic rifle parts, police said, hidden inside a toolbox.
That was sent to an address in Birmingham, albeit without the gun parts.
The original package, forensically marked, was discovered by officers at the time of Iqbal's arrest, while a phone whose number featured on the second package was discovered in his car.
Speaking after sentencing at Birmingham Crown Court, NCA operations manager Niall Conner said the operation had "taken items including gun parts and a 3D printer out of circulation, which could have been used to create deadly weapons for use by organized crime groups".
"The supply and use of firearms has a devastating impact on public safety and are used in acts of intimidation and serious violence," he added
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