YUBA COUNTY (CBS13) — Three men were arrested at a gun range after an alert man noticed something wasn’t right about their cache.

The Yuba County Sheriff’s Department seized a collection of illegal weapons and ammunition at the Spenceville firing range, including an illegally-modified Glock handgun, and two AR-15s—both custom-built, one fully automatic.

“The two rifles that were seized were just illegal in nature because of the length of the barrels, and the overall length of the gun,” Yuba County Sheriff’s Lt. Wendell Anderson said. “Three of the weapons had no serial numbers; we were unable to track them whatsoever. One of the handguns did have a serial number, but it was unregistered.”

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Deputies are tracking whether that gun is connected to any crimes.

The three men caught with the weapons are under arrest. Angelo Craver, Marquis Miller, Bobby Yettou face a list of charges including manufacturing of machine guns. Yettou is a convicted felon and known gang member.

One of the men told deputies they learned to make the weapons on YouTube.

The tip into the sheriff’s department came from a man with military experience, who was also at the Spenceville firing range, and who identified the illegal weapons, removed his family, and called the cops.

“He had expressed concerns over the manner in which they were operating the weapons, and the direction that they were shooting the weapons,” Anderson said.

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So far deputies have no evidence the three were planning to use the guns to carry out any crimes. That is a possibility they may never know.

“Anytime you can take an illegal weapon off the street it’s a good day for us in law enforcement, and the community,” Anderson said.

Illegal, high powered, homemade, fully automatic weapons, in the hands of a convicted felon and his friends—now they’re all facing new felony charges.