A 19-year-old Jacksonville-area man is facing federal charges after prosecutors say he used a 3-D printer to churn out illegal machine-gun conversion devices and sold dozens of them to an undercover buyer for a few hundred dollars. Emani Rey Justavino was temporarily detained on Sept. 10 after a federal criminal complaint accused him of illegally possessing machine guns and possessing unregistered weapons.
According to a Yahoo News report detailing the federal complaint, an undercover ATF agent and a cooperating source first met Justavino at a northwest St. Johns County restaurant in August, where he allegedly arranged for four of the 3-D printed devices to be obtained from his roommate at a home off Lake Mandarin Circle for $200. The same report says that a day later, Justavino claimed he had printed 50 more of the devices — known as machine-gun conversion devices, or MCDs — overnight and had run out of printing material, then allegedly handed an undercover agent a box containing all 50 for $300.
The News4JAX account of the same court records describes how the case took shape: an ATF task force officer learned that a person identified only as J.B.J. was advertising the devices on Instagram, and investigators later learned of Justavino through an Instagram seller.
How the Undercover Buys Allegedly Unfolded
Court records reviewed by News4JAX lay out a two-day sequence in August. On the first day, at a northwest St. Johns County restaurant, Justavino allegedly arranged for four devices to be obtained from his roommate at a home off Lake Mandarin Circle. The following day, at a location not identified in the provided accounts, he allegedly handed over 50 devices packed inside a toaster pastry box and agreed to sell all of them for $300, according to the same court documents cited by News4JAX.
The complaint also includes allegations that Justavino possessed machine guns and unregistered weapons.
Why Conversion Devices Draw Federal Scrutiny
The devices at the center of the case, often called Glock switches, are small attachments designed to convert semiautomatic firearms into fully automatic weapons. The Yahoo News report notes that the September 3 complaint states a converted semiautomatic Glock pistol can fire about 1,200 bullets per minute with a single pull of the trigger.
The surge in these devices is not unique to Justavino's case. According to WTOC, law enforcement nationally has seen a 570% increase in finding guns with conversion devices attached at crime scenes, with ATF seizures climbing from 814 devices between 2012 and 2016 to more than 5,400 between 2017 and 2021. An ATF special agent told the station the devices are generally printed in less than five minutes, which has prompted the agency to train state, local and federal investigators on how to spot them at crime scenes.
Other Cases Show a Growing Pattern
Florida has seen larger versions of this alleged scheme before. The Yahoo News report notes that Clay County resident Kristopher Ervin was sentenced in 2023 to 68 months in prison for selling roughly 6,600 conversion devices. Elsewhere, KCTV5 reported that Kansas City man Dalton R. Johnston was charged in 2024 with possessing hundreds of homemade devices, allegedly telling an undercover agent he could 3-D print 45 at a time, in up to three batches a day, and had sold 300 devices while offering to make 500 more within a week.
Justavino has not been indicted as of publication, according to Yahoo News, and if convicted he could face up to 10 years in prison. U.S. Magistrate Judge Paricia Barksdale ordered him temporarily detained while the case proceeds.
