Peter Robert Berry was also indicted and charged for possessing firearms as a felon.
Damien Lashaun Nelson had others purchase firearms for him illegally between June and October of last year.
Charles Sauke, 22, pleaded guilty to possession of an unregistered firearm in federal court.
Dayne Adrian Sitladeen pleaded guilty in U.S. District Court Wednesday.
Because of a previous felony conviction, Phillip Jones Jr. was prohibited from purchasing or possessing a firearm or ammunition.
More than 100 people have been injured in shootings in the Twin Cities since Memorial Day.
The change comes four years after Philando Castile was fatally shot by police during a traffic stop during which he said he had a gun.